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1.
When a drunk person is persistently looking at you out of the corner of their eye.
"Boy I could feel John sideballing me all night while I was talking to Bill, he's got to get over it!"
by BRC October 06, 2005
11 1
 
2.
To look out the corner of your eyes at someone so that they "can't tell your looking"
I changed my radiator in the parking lot of the apartment complex. Noone said anything, but alot of people were sideballing.
by Tug33 May 18, 2011
6 1