When you yawn and you get a painful cramp in your jaw/neck area. Sometimes it's so bad that you cannot close your mouth for a bit. It's called cocksucker's cramp because of the expression one does after yawning when he/she realizes she got a cramp it that area.
Chad : Matt yawned and his mouth stayed open for like 2 minutes.
Dan : LOL, Cock Sucker's cramp!
Typically a mouth breather. When the person goes about their day with their mouth slightly open and never fully closed.
Tommy has cock sucker's cramp. He walks around and does his shit with his mouth half open all the time. Probably from sucking so many cocks all the time.
The facial expression locked in a sucky sucky position. Often referred to in a joke with a punch line...do you get it? How often?
My co-worker asked me this joke. I kicked his ass, and as he laid bloodied on the floor I told him never to tell me the "cock suckers cramp" joke again.