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 answer][1]. 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.  


  [1]: https://english.stackexchange.com/questions/23763/what-is-the-origin-of-the-phrase-cut-the-mustard