stage-door Johnny

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic A man who is infatuated with one or more theatrical actresses and who routinely lingers in and around theatres in an effort to meet and form relationships with the female object(s) of his affection.
• noun idiomatic A devoted fan of live theatre and of performing artists, who habitually spends time in and around theatres.