Where a boy/man moves onto the '
bases' on relationships frequently or too quickly. eg first base (
kiss)
second base (oral) so on.
Preferably moving quite frequently, onto many girls, doing sexual activities. Known also as a player.
Harry: I got sucked off by Kirsten yesterday night, but the day before fingered
Katy in a bush!
Martin: Harry you baseman!
Or
Cindy: Did you hear that Harry got head off Kirsten but fingered Katy and tried to have sex with Marie!
Laura: Ew, OMG, what a baseman