Technically, the first time they kissed was on the planet Ghiloushaphunmishaekh - or Fred, as Rose liked to remember it. After spending well over a minute trying to pronounce the name, the Doctor had rolled his eyes and muttered "let's just call it Fred." She still wasn't sure about the quick burst of emotion that flashed in his eyes when she had readily agreed, but the name had stuck nonetheless.
Whatever the planet's name, they apparently had strict rules about couples - no matter their sexes - being seen together in public. Singles were fine. Groups were fine. Pairs, on the other hand, were only allowed to be seen together when they were married, and the only way to prove that fact was with public displays of affection.
Very public displays of affection.
The Doctor gave her a reassuring wink as he leaned in so that they were face to face. "Sorry," he said softly. "No other choice." Then he kissed her, as chastely as her mom had every night before bed when she was growing up.
Something deep inside her felt as if it suddenly burst into flames.
When he pulled away, Rose knew that her face was burning bright red. It faded, though, as his hand slid down and gently took hold of her own. With that one single action, normalcy slid back into place.
Approximately five seconds later, they found themselves being herded toward the imperial palace in the middle of the city. It didn't take long to figure out that the locals had taken her embarrassment to mean they were newlyweds, which not only meant they got to meet the leaders but also free food. Neither the Doctor nor Rose felt inclined to argue.
Then the Doctor insulted the emperor's brother ... or possibly his wife, which - looking back - would have explained everything except the full-length beard he (she?) had. Either way, their hosts went from bending over backward for them to waving very nasty looking guns in less than thirty seconds, forcing yet another sprint toward the TARDIS with an angry horde behind them.
It was either amusing or alarming how often that happened. Rose wasn't quite sure which to choose.
As the TARDIS doors whirred shut behind them, Rose felt her legs tremble. She let herself slide to the ground, pulling her legs up under her. And then she started to laugh.
She wasn't sure whether it was relief or hysterics, though the Doctor apparently thought it was the latter since he was quick to drop down beside her with an obviously panicked look on his face. Rose quickly decided that it was definitely relief.
Of course, that realization only made her laugh harder.
After another minute or so had passed, the worried look on the Doctor's face had changed into a suspicious one. And then a resigned one.
Then Rose suddenly leaned in and kissed him. They both pulled away almost instantly, her laughter disappearing in a second as surprised looks appeared on both their faces.
"Sorry," she choked out, her face reddening again. "I don't know why I just did that."
The Doctor just stared at her for a moment, both his face and his eyes unreadable. Then he slowly started to smile.
Their second kiss counted. As did their third, and their fourth, and their fifth...