Megatron's is very likely to be "Here's a hint." (Which now that I think about it is just so defining as a character moment: "You know that guy who put up with your shit for the last million years? No more.")

Yeah. I still remember seeing that for the first time when I was, like, seven, how much of a shock it was. (Not as much Optimus dying, though.)

I think mine is Starscream getting jealous of Nightbird. But I am odd.

I love that one too *g*. Especially since there's really no non-slashy way to interpret 'she's hot enough to replace you.' I mean, she can't fly, so it's not like Megatron means he's going to make her Air Commander! And it leads to Starscream actually slapping Megatron out of sheer bitchy jealousy.

I also love the tackle-pounce-hug from the end of A Decepticon Raider in King Arthur's Court. No, Starscream, he is not pleased to see you.