Another contributor objects to the 'wedgie' definition and sent in the following:
In my school described the action of grabbing someone's testicles and twisting (especially when performed by a girl to get revenge over some form of sexual harrasment). One girl, Kim, a couple of years above the contributor, was notorious for giving them, although he personally found her to be a very nice person. Used as "Watch out fer that Kim, she'll melvin yer!!".