The use of the indefinite it is common, as in the sentence
He can't get it up!
Less common is an expression used in the play "Cat On A Hot Tin Roof":
"[He] can't cut the mustard."
See this answerthis answer. In other words, the man with E.D. is not up to the task. This phrase is used more widely without the sexual connotation, as in the following sentence:
Even after months of physical training, the runner couldn't cut the mustard in the marathon.
In other words, he couldn't "make it" as a marathon runner.
