None of the available choices fits for me. I see the expression as “mischievous,” specifically that he appears to be observing something and is perceiving the opportunity for a prankish response or followup.
I’d say it’s an enthusiastically pugnacious anticipation — you know, like Popeye, or a guy at the end of the bar cheerfully asking you if you want to repeat that to his face.
I voted “Other” and without having read the answers so far (and without knowing the painting), I see a guy who’s satisfied and happy about a deal he’s just done with the person he faces and we don’t see. There’s also a bit of glee, because maybe he took them to the cleaners.
Agree w most of the folks above. He’s a shrewd player who’s just finished setting up the kill and is watching the victim walking right into the trap. It’s happy anticipation of something bad about to happen to somebody else. Whether that’s an assassination, or simply losing a poker hand to a stacked deck I can’t say.
I wonder if there’s any connection between the motivation for this question and the motivation for the OP’s avatar? I actually half-expected the poll to be about his avatar, but the parenthetical ruled that fun idea out.
Maybe @Peter_Morris should have another poll: What means the expression on his avatar’s face?
Does the ambiguity derive from the fact that you can’t see the edges of his mouth? I think my brain seems to want to fill in a downturned mouth in a sneer, but I can force it to put in an upturned mouth instead, which changes the expression considerably, into something more like smug satisfaction.