A Chubmeister is a person who is a, for example, loser or is stupid. It can be used loosely. It can also mean someone who has a lot of chub (fat, who is fat). It can also be used as a playful insult, teasing.
It can be used as a noun, verb, or adj.
She's SUCH a chubmeister!
Look at him chubmeistering across the street! What a loser!