"See, I don't know where you get the idea I'm anything but straight-laced."

Chuck gives off the impression of being short and belligerent, but really he's just the second.

It's probably how he squares his shoulders and faces the world like he's probably going to headbutt it.

Anyway, what we're saying is, Shephard's still got a good two inches on him, and Chuck's not beyond using his headstart to 'accidently' block his path.