I think the only times this happened to me were after a long night of coke or booze. Although, the coke notsomuch.

Thinking of one ex in particular, 100% of the time he got drunk he was impotent, and whenever he ran out of drugs/money he couldn't get it up...

As for guys failing to deliver in general...100% of guys have made me a promise, and 100% of guys have failed to deliver.....