Munchkin has become too subjective of a term lately. Generally, I define it as using rules exploits and outright cheating to break the game, with the goal of dominating game play at the expense of everyone else's enjoyment.
Munchkin is really more a style of play than anything else, so it is hard to tell whether a character is munchkin simply by looking at a build. If a character is built solely for combat, neglecting mental Attributes, social skills, and other skills unrelated to combat, that character could be a munchkin. But it could be someone who simply isn't interested in the non-combat areas, or someone coming from a game where the players had to min-max simply to survive. And again, it's a question of playing style. There is a difference between a killing machine who protects the noncombattants in the group, and a killing machine who starts a fight during the meet with the Johnson because he is "bored."
It's hard to tell whether this character is even a powergaming build, without being able to see more than raw Attributes - skills and powers/'ware would give a more complete picture. I would be able to tell if the character had non-combat skills or not. I would be able to tell if the character has any extra initiative passes or ranged skills - he might be a walking tank, but if he only goes once a round and can't retaliate against distance attacks, he wouldn't even be that effective in combat. He would squash anyone who got near him, but compared to a street samurai hosing down people with auto-fire over several initiative passes, he wouldn't be the most optimal build.
