From personal point of view it depends who is saying it, and how they are saying/asking it
If someone was to shout 'gay boy' at me, I would take offence
If someone was to ask 'are you gay?', that is completely fine and I would never expect them to ask if I was 'homosexual' or LGBT(Q) etc
The problem with the word 'gay' is when it's used to mean stupid. E.g 'That's so gay'
If someone calls you a homophobe for asking 'are you gay' obviously without malicious intent, then they're over-reacting in my books
Edit: The necessity of some people to ask someone if they're gay or not is a whole other point