1)to ejaculate on something or someone
2)to get ones menstrual period (this expression is used this way in certain parts of the UK)
3)to come online, particularly to sign into an instant messaging program, to enter a chatroom, etc.
1)If you pull out, don't come on the quilt my grandma made me.
2)You seem a bit moody today; are you about to come on?
3)I wish Fox would come on so I can kick her ass at literati.