I don't like butch women but they're relentless?

My girlfriend and i are both very femme and i think that is one of the reasons why whenever we go out together, no one believes we're a couple. Last night three different butch women came onto me in Manchesters gay village and when i said i was taken and i wasn't really into butch they just kept on coming. It p's my girlfriend off and she nearly punched one of the women. I had to pull them apart and then when we got home my girlfriend had a go at me and said that i lead them on. How the hell did i lead them on and what can i say next time to get them off my case?