To retract what you have previously said. Used by the Police (unofficially) to describe the actions of a victim - usually of domestic assault, who initially complains resultig on the offender being arrested, but then changes their mind and welcomes their tormentor back with open arms.
After one or more people has peed into a toilet, and before the toilet has been flushed, a victim (normally the person who peed)will have his head shoved in the toilet, and while his head is in the toilet, the executer of the swirly flushes the toilet.
"He had just peed, so I gave him a good, old-fashioned pissswirly."