When a girl has given enough blowjobs, and her knees are red and bruised from being on them so often. Can also happen after a single very long blowjob.

Can also occur after bumping into things, falling over etc.
1) "That girl has a s serious case of blowjob knees"

2) "I fell while drunk yesterday, I look like I have blowjob knees"
by Cap'n Crimson July 6, 2015
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