Overly Bragging Excessive Coolness. Used to describe somebody that is waaay too full of themselves and think that they're "all that".
Pronounced with all the letters flowing together, so it would be "obec".
In a game of dodgeball, an O.B.E.C. stands on one side, an opponent stands on the other.
The opponent throws the ball and misses. The O.B.E.C. throws the ball and just barely hits his opponent.
O.B.E.C.: "Ohhhhhh yeah did you see that shot? That was pure skill! You, my friend, are OUT! OUT OUT OUT OUT!"
Opponent mutters to his friend: "He's such an obec."