Roadtrips are fun—simple enough to pass the time. Katsuki won't admit it, but he savors these soft, quiet moments, like this ride in the dark. Everything is peaceful.

With Izuku behind the wheel, he drives at an easy enough pace as to not wake up Ejiro, who has his legs sprawled in the seat—he's taking up 90% of the backseat—as he leans his back against Katsuki's shoulder. Ochako has taken the passenger seat, talking softly to Izuku. Some lovey dovey crap he never cared for. You, however? You're stuck perched on Katsuki's lap.

You see, the car actually isn't very large when Ejiro is lying in the backseat, leaving Katsuki a sliver of the far left seat. You had nowhere to sit, so on his lap you go. He's fine with it, he thinks.

When the unpaved roads get bumpier, Katsuki grunts uncomfortably, trying to keep Ejiro asleep against him as Izuku murmurs a quick apology—the damn nerd. You're trying not to jostle all over his lap, but each pothole has you shifting in his lap. You have no choice, really. And it's even worse that you haven't exchanged any words, he's just been idly scrolling on his phone while you watch on, because he'd hate to wake his best friend.

With another bump, you lift in his lap again, and this time, you feel something that wasn't there originally. A bump..? No, it's nothing like that, and his pockets aren't there–

It's his dick, you realize soon after hearing the soft "mmmh" with his exhale. And he knows you know when you go still.

".. Shit, 'm sorry," he mumbles into your ear, suddenly feeling awkward. You're his friend of years, and here he is, getting all hot and bothered because you jostled on his lap a little. It's not either of your faults that you were forced to grind all up on him! And it's not his fault he's a virgin! You'd think he'd get laid with his looks, but he's saving it for someone special. "It's- ah... um, just- a reaction.." he adds in a mutter, looking over to Ejiro still sleeping against him. He'll have to be quiet.