Artificial knees made for people with weak/broken knees so they can do everyday stuff like us. A famous example is the streamer YourRage as he uses bionic knees because his own knees don't work anymore.
Person 1: Ah man I broke my knees the doctors said I'll never be able to walk again.
Person 2: Just do like YourRage and get a set of bionic knees.
Slang that originates from America in the 1920's. Similar to today's cool.It expresses a state of excellence in an item or action, but generally not a person.
What one gets when giving a blow job while kneeling on the carpet. The knees get dry/ashy and impressed with the carpet weave pattern. Not as serious as rug burns.