Def. 1: Used to describe something particularly
easy, generally a task.
Def.2: Used to describe someone of the opposite sex, particularly in how easy it will be to pick that person up. A sure thing.
origin: beginner's little league
game of the same name, where the degree of difficulty in hitting a
baseball is reduced by placing it on a tee for the child to hit.
"I know the
guy who runs that place, so getting our
friends in should be teeball tonight."
"See that
drunk chick over there? Total teeball."