Depending on who is asking and the situation (an earnest question from a peer versus a spurious question shouted from another vehicle in reference to a bumper sticker on my rig, for instance) it is sometimes useful to reply by asking what the questioner means.

You mean "gay" in the political sense -since it is largely a political label?
No, no --the usual reply comes-- "gay as in men who have sex with men."
Ah! So, a man who has never had sex with another man cannot be gay? And men in prison who have sex with each other are all gay?
No! No, er, I mean, well....

The point made that it is not so simple a matter as may have been assumed, I reply that at various points in my life I have both been in love with and enjoyed sex with both men and women, and for a very long time my partner --together with whom I have raised our kids-- has been another man. What matters most to me is that my partnership and family are second class citizens without equality under the law, disenfranchised from civil marriage, equal immigration rights for spouses, open and proud service in the armed forces (including access to all the taxpayer-provided benefits which come with such, from college funding to VA medical care), so if others want to call me something then far more relevant and accurate as a functional descriptive than "gay" or "queer" or "bi" would be "second class citizen" -because this is truthfully the plain fact of the matter as my partner, kids, and I experience it day to day.

By the way, when I am invited to heterosexual friends', coworkers', and relatives' weddings I congratulate them and decline, saying "When I can invite you to my wedding then I'll come to yours, but as much as I love weddings I have not been to one in over 30 years because I will not willingly watch others take advantage of a double-standard denying equality to me and my family, so thanks but no thanks." This one action, more than any other, has really rocked people back on their heels -and when it finally sinks in that I am not angry with them but rather with injustice, has really won over some among them as genuine allies and advocates for equal treatment under the law.