I went to a lesbian club once with my buddy when we were teenagers and it took me about 3 minutes to figure it out. The gi-normous sign inside the club that said "THIS IS A GAY/LESBIAN BAR," etc. helped.
I had to literally drag my friend out of the club. He didn't see the sign and thought he was in heaven (an all female club). Didn't matter to him that a few women nearly slapped him in the face. 

That's hilarious! It would have been priceless to have seen him futiley trying to work that room.
There was no sign over the door at the place she took me to. Infact, there was only one guy in the entire place.
He was very flamboyantly gay too. There was something that just felt odd about the place... it just didn't seem quite right to me. It took me a while to realize... "Hey, there are no men in here". Then I immediately saw a man with huge biceps in a lumber jacket with the sleeves cut off, kissing his girlfriend up against the pool table. As he turned around, ...I realized the lumber jack had big breasts along with his big muscles. {lol} That's when it dawned on me. I began to put things together and realized I was in a lesbian bar. I just thought everyone was so laid back & friendly.