Lambert doesn't move away at Psi's approach. Honestly, if he wanted to punch him, he's welcome to try -- it's a normal enough reaction, from Lambert's perspective. At any rate, a little physical violence always helps Lambert work through his frustrations; why wouldn't it do he same for anyone else?

A better person would try to understand where Psi's coming from, might know the right thing to say. You're not the only one who's ever lost someone, or You should hang on to all the memories you can, or even I know what it's like to feel helpless.

Instead, what he gets is: "Why don't you make me?" Lambert's still smirking, but there's a sardonic, bitter edge about it, cynical rather than truly amused.