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1.
When a female has performed oral sex on a male and does not remember the experience. Even after presented with evidence she denies ever performing the act. Must not be under the influence of drugs or alcohol.
Dick and Jane were in a long term relationship. But one day Jane went over to John's house and gave him head. John told Dick, and Dick confronted Jane. Jane refused to believe or admit that she gave John oral. Jane has been diagnosed with Cock Amnesia.
by Pace' September 01, 2006
 
2.
When you go perform Felatio, or any other sexual act and can't remember it.
Thorn, "Did you have sex with John Doe?"

Carrie, "I am sorry I just can't remember."

Thorn, "So you are telling me you have Cock Amnesia?"
by Minnaar August 31, 2006