What is Sugarbowl?
The act of engaging in a purely physical/sexual affair with a significant other of a friend or acquaintance. The friend or acquaintance must have no knowledge of the affair. It can be a one time occurrence or an ongoing affair, however, a deeper relationship can not occur, it must be kept purely physical.
When used as a noun, it describes the offending partner of your friend/aquaintnace.
Ian dipped his finger in Jean's sugarbowl.
Ian had sex with Jean's girlfriend.
I bet Ian will be sugarbowling tonight!
I bet Ian will be having sex with Jean's girlfriend tonight!