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1.
An extreme fetish or sick mental twist that affects certain people. When these people affected see an ugly person, someone so ugly that NO ONE would have sex with them even under extreme intoxication, they begin to fantasize what measures would need to be taken in order to lay the unfortunate looking person. The most extreme situation (where the syndrome got its name) is when the person would only be able to lay them by sticking the person into a sleeping bag entirely, zipping it up over thier body, and cutting a hole where thier crotch is, humping and having sex with the live person inside of the bag.
1) "There is no way in hell I would do old lady!", G-Man proclaimed."That is...unless...I apply my sleeping bag syndrome."
2) The man infected with sleeping bag syndrome jammed the ugly midget into the sleeping bag, zipped it up, and humped it while simotaneously throwing up in disgust.
by Ashley the Amazing July 17, 2006
 
2.
Refers to an uncircumsised male penis, since it resembles an unrolled sleeping bag.
"Have you seen that Bob's got the sleeping bag syndrome? What a turn-off!"
by Erika Butler June 10, 2008