How to get out of a vehicle?

[McDonald's]

OK, I know this is probably coverred in the training mission, but while trying to get to that part I got stuck at throwing the grenade into the window and had to exit because of urgent business THREE TIMES (it just won't allow dropping the window ), so I'd rather get the answer here.

I tried the action menu after stopping the truck, but after clicking it twice all I got was the animation of the guy climbing back in, as if he got out, but he didn't. And after that no button worked. Is this by any chance a glitch?

Well, I'll TRY to finish the training mission one more time without having to interrupt it , but in the meanwhile, what can you say?