A) Realize you should not have done and will never consciously do again, or
B) Acknowledge doing, but got too wasted to clearly remember.
Sidenote: Is commonly used just before Not so much.
"Yeah... yeahbutno. Not so much."
B)"Dude, you were wasted, you totally got with her. Don't you remember?"
"Yeah... Yeahbutno. Not so much."