"Mom and Dad are gonna be pissed." Had Dipper's grip been any less firm on the windowsill, he probably would've fallen on the floor.

"God, don't do that!" Dipper hissed, whipping around to find Mabel sitting on the end of his bed.

"Please, there's no need for formality. Call me Mabel." The girl grinned, completely unperturbed by her twin's increasing glare.

"You are sincerely hilarious." Dipper intoned, placing both his feet quietly on the floor and shutting the window behind himself.

"Aren't I?" Mabel flopped back onto the comforter, her ever-long hair splaying around her like a curly halo, "But enough about me; let's see the damage."

"Well, I have an empty wallet, a tin of antibacterial ointment, and a very large bandage." Dipper pulled up the sleeve of his hoodie and waved his forearm over Mabel's face.

Mabel let out a low whistle. "Yep, Mom 'n Dad are gonna be super pissed."

"Yeah, about as pissed as they'll be when they hear you've decided not to go to college." Dipper snorted.

Mabel sat up and shrugged. "Well, you're gonna be there as my backup when I tell them, aren't you?"

"Of course." Dipper replied immediately as he pulled his sleeve back down.

"Good," Mabel nodded, then turned and punched her brother in the shoulder, "Just like I was supposed to be there as emotional support when you went to get your tattoo, you big jerk!"

"Okay, ow," Dipper whined, rubbing his shoulder.

Mabel ignored him. "Why didn't you wait for me?" She demanded.

It was Dipper's turn to shrug, glancing away. "It's the day after our birthday."

"So? What's that got to do with anything?" Mabel rolled her eyes.

"So, it's the same every year. We spend our birthday together, celebrating with family or whatever, and then the day after we go do whatever we like separately."

"I know that," Mabel jabbed Dipper in the side with her elbow, not hard enough to hurt but enough to make him flinch at the coming blow.

The tradition of spreading their shared birthday out over two days had been a standing one since their 14th. The day of their actual birthday, they spent eating cake and opening presents and decorating for a party that was largely orchestrated by Mabel and doing all those traditional birthday things. The day after was theirs to indulge individually; whether that meant taking birthday money to the mall and spending it all in one place like their birthday cards told them not to or just sleeping until noon and eating leftover cake for lunch was up to them.

Usually, Mabel would go out and spend the day goofing off with friends, shopping or going on a day trip somewhere and "having fun, Dipper, you should try it sometime!"

Dipper would spend his day in almost the opposite fashion, holed up in his room reading whatever new and interesting books he'd received or heading out to get whatever he'd really wanted with birthday money, or possibly spending quiet time in a secluded corner of the park, which "is absolutely not creepy, shut up, Mabel."

Both days were enjoyable, and even if the other didn't always understand the where or why their twin spent their day-after, they never wanted to disrupt the tradition, which was why Dipper could only shrug and mumble at Mabel. "I didn't want to bother you, I guess."

"Psh, what do you mean, 'bother me'? You think I don't want to come see you try to keep a straight face while getting repeatedly stabbed with a needle?" Mabel scoffed, throwing her arm over Dipper's shoulders.

"No, I just- I dunno, you always spend the day with friends, I didn't want to pull you away from that just to come sit in a tattoo parlor with me when you wouldn't have anything to do there, anyway."

"What! No way, you only get to do a rebellious 18th birthday thing once! I totally wanted to come!" Mabel cinched her arm more tightly around Dipper and shook him, "Don't do that thing where you make decisions for me because you think you know better!"

"I wasn't making your decision for you! I was being polite and not bothering you!" Dipper huffed, "You're welcome."

Mabel scowled over at Dipper, who attempted to hold a look of haughty indifference, but the charade only lasted about half a minute. Mabel burst into snorting giggles, burying her face in Dipper's shoulder, while Dipper huffed out some squeaky chuckles and wrapped his arm around Mabel's back. "It's been 18 years, Dip!" Mabel stuttered around breaths of laughter, "How do you not get that you're not bothering me, like, ever?"

"I don't know," Dipper shook his head, attempting to dispel his burst of laughter like hiccups, "Next one you can totally be there for. I promise."

"Duh!" Mabel sat up and gave Dipper a gentle shove, "And next time we're just gonna walk out the front door instead of climbing out your window and down the tree like creepers."

"Eh, depends on how fast I can save money for another tattoo. Might still have to sneak out at that point." Dipper tilted his head in indecision.

"Maybe," Mabel shrugged in return, "But I get to design the next one, right?"

"As promised," Dipper nodded, "But I get veto power."

"Psh, you're no fun," Mabel waved her hand at Dipper dismissively then made a grab for his arm, "Okay, now lemme see."

"It's still kinda raw," Dipper warned her even as he pulled his sleeve back up, "So it doesn't look completely like it will once it's healed…"

"Yeah, yeah, I got it, show me the ink!" Mabel demanded.

"I'm working on it, sheesh." Dipper hissed a bit as he pulled the bandage back from his forearm to bear the fresh artwork to his sister.

Mabel gasped. "It's perfect. It's exactly like your drawing! Except more inky and kinda painful-looking right now."

"Yeah, I think it came out pretty good." Dipper grinned, eyeing the lines with pride, "And once I save up enough, I'll get something on the opposite arm."

"And I'm gonna be there!" Mabel declared as Dipper pressed the bandage back down, "And I'll only laugh a little bit at your pain."

"Don't make promises you can't keep, Mabel." Dipper shook his head fondly.

"Okay, yeah, that was a lie. I'll laugh a lot." Mabel grinned, "But I still love you, Goober."

"And you make such a compelling argument for it."

"Don't ruin our awkward sibling moment," Mabel insisted, giving Dipper another shove, "Just say you love me, too."

"Okay, alright," Dipper put his hands up in mock surrender, "If it'll stop the violence, I love you, too."

"Yes! Love confessed under duress still counts!" Mabel punched the air in triumph and Dipper laughed.

They sat in amiable silence for a few moments before Mabel, as ever, was the one to break it. "So when are you going to show Mom and Dad?"

"Uh, I was planning on maybe… never?" Dipper glanced away, "I'm just gonna keep wearing long sleeves for as long as I can get away with."

"Wimp." Mabel teased.

"Okay, fine. I'll save it for when Dad asks you if you've applied for any colleges yet. That way we can be grounded together."

Mabel grinned. "Deal."

-/-/-

A/N: Inspired by two different pieces of fanart. I can't link things through here, but if you want to see the pictures I had in mind, this story is posted under the same title and username on Ao3