This phrase is used by guys to pick out attractive girls. If a guy says to you "You're on my team" it means he finds you physically attractive. A variation of this would be "She's on YOUR team" which means that a guy finds you so unattractive he puts you on his friends team.
Guy to girl: You're on my team!!
Girl: *punches his lights out*
by SpoonBalancer September 18, 2007