Seriously?! What is wrong with a guy asking another guy over for coffee? If the friend is gay he's unlikely to rip your clothes off the moment you walk through the door and is more likely going to swing the 'you're not gay, are you?' at some point to test the waters. You'll simply reply, 'no', and quietly get get on with your coffee drinking and hobby-ing.
This thread illustrates the difficulties faced by gay men (and women, I believe) on a daily basis: prejudiced and ignorant opinions that can be downright hurtful. Essentially many of the posts here boil down to the inability of gay men to contain their sexual advances, are sex crazed maniacs that find any and every other male attractive and worth pursuing for sexual pleasures. Even if the friend is interested in pursuing something how is it so difficult for you to say 'no thanks' and get on with your life? The poor guy has probably been in a world of torment getting the courage to ask you around in the first place, being so fearful that maybe he's read you wrong.
If every gay man stayed at home and never asked anyone around for coffee unless they had a flashing gay light on their head then there'd be a bucket load of lonely people out there. Oh wait, there are, because of over-reactions like this one.