After my latest fanfic I wanted to write something lighter again and this idea came up. I remembered how, in the movie, those two seemed so adamant in going in a straight line, something that has never been referenced at all in the show. So I wondered what could be a likely explanation of why they decided to go on a straight line up from a certain point. Here's what I think happened.

Operation Impending Doom 2 (OID2) was going perfectly well, planet after planet was falling to the irken empire. The two leaders of this seemingly unstoppable invasion force were not just a little bit smug about it. Little did they know that they would have a problem very soon.

Almighty Tallest Red and Almighty Tallest Purple are at they usual spot in the ship's bridge, eating snacks, joking together, having friendly banters with each other, all in all a normal day.
Until one of the pilots turns toward them "Sirs, What will be our next destination ?"
Purple seems a bit surprise to be asked this "Just look at the program for OID2, our course is detailed there" he even seems a bit annoyed to have been interrupted in his fond recollection of past conquests with Red for this.
"But, my Tallest, we came to the end of the course you gave us at the start of OID2, there is no instructions as to what we are to do now"
At this the two taller irkens look at each other, they had completely forgotten that this would come someday. Quick, they had to find a suitable answer to their subordinate's question, just telling the truth would make them seem a bit less competent because they should have planned for this. They look at each other for several long seconds, but this silent stare didn't give them any solution, just confirmed to each that the other realize the problem they have. Everything was going so well so far, if it continues like this they'd be remembered in history along some on the most important tallests to have ruled, they had to find something.
The long silence slowly attracted the attention of the rest of the bridge crew, now everyone was looking at the two leaders, waiting for an answer, an orders to follow.

Red turns back toward the large glass panel that shows space, he has an idea. He lifts his arm slowly and purposefully, extending a finger toward outer space "There, we are going there". Everyone, including Purple, look at him with some surprise and puzzlement. This wasn't enough to convince anyone so Red continues "We are going to continue in this direction, conquer anything in our way. Bring up the galactic map !" the galactic map was immediately brought up, hiding the view of space. Red goes in front of it and trace with his finger a straight line going from the Massive's current position to an edge of the galaxy, in the same direction he pointed "This is our course, got it ?"
One of the pilots dares to speak up his confusion "A straight line ?"
Red glares at him, one more word and this one is going out the airlock.
Purple got what his friend is trying to do by now and adds to this plan "Yes, a straight line. It will be symbol of our determination and the inexorable will of the irken empire. Everyone along this line will shake with fear as they'll expect our coming but know they can't stop us"
The same pilot (apparently suicidal) still has a question "But this course makes us go through several stars and planets"
Red wordlessly gives the order to throw this one in outer space "I know that, and I also know that the Massive is more than capable of annihilating anything blocking its path" Another anonymous irken walks in to take the now vacant seat.
It's with a tone of finality, a tone that don't accept any contradiction and don't leave any doubt that this was their plans since the very start, that the two order to start following this course.

.

Some time later

Red and Purple are alone when Purple thinks back on what happened earlier that day "A straight line ? Really ?"
Red doesn't seems phased by this notion "Yep, got a better idea ? We couldn't just tell them we had no idea what we wanted to do now"
"Of course not, but now we're kind of stuck with this random course, we didn't plan it through, most of those planet haven't even been prepared by invaders"
Red shrugs "You feel like going back and telling them we made a mistake ?"
"No, we can't do that neither"
"Then I guess we re going in a straight line"
"Guess so"
And so they did.

So, what do you think ? Is it a likely explanation to you ? Or maybe you have a better idea, then tell me.

Anyway, I hope you enjoyed this fic, I wrote it hoping it'd be funny no matter if you share my explanation idea or not.

I know it's short, sorry.