If you are verbally telling them that you are gay but acting and interacting with them in a totally opposite way, they wont seriously think you are!
Don't tell them, show them
Imagine a situation when you would see a guy get off of a 2011 Nissan 370z, with Ray-band's glasses, gold watch and lacoste's shirt... Now, if he comes to you and tell you he is really poor, will you believe him? Chances are he's not.
Personally, I was telling them I was gay and bullshit, but the girl I was picking on told me she didn't believe me. Saying something and acting differently will totally mind-fuck the girl.
While she probably knew I was not gay all the time I was flirting with her, her protectives friends didn't saw me as a "treat" until I was actually hooking up with her.