Starscream's mouth pulls back in a dissatisfied sneer, because he actually was gunning for the jealous reaction, because then he'd at least get to feel superior here, in a situation where he has far less control than he'd really like. How can Megatron not be jealous?? The only reasonable conclusion is that the Starscream here really is that bad, which makes Starscream feel simultaneously better and worse about himself. Hm.

"Fine," he says, just a little bit petulantly, but mostly to change the subject to something he is actually keenly curious about. "So if you loathe your Starscream so much, then how did he get to be your second-in-command?"