Maybe you are tired of the bar scene or just looking to network with other gay men.
(Some people say they only use Grindr to make friends.
These people are liars.) I myself have it on my phone¹, probably because it feels less weird than Craigslist's casual-encounters section², and I've often shown it off to my straight friends.
It is not so tricky to start flirting with a straight guy.
As a bisexual or a gay companion, you stand a better chance than all other women out there. A straight guy may be interested in another man simply because he does not want to fall into traps of a relationship with a woman.
While this may not exactly mean that he is attracted to you, it definitely means that he is looking at you as his confidante, a friend to share the good and the bad times.
You may consider that your flirting is nearly successful at this point.
Every single one has the same two reactions: one, it's too bad there's no straight version of that, and two, a straight version would never work.
Well, now we have a chance to find out if they were all right, because the people behind Grindr have just released Blendr, the heterosexual version with an infinitely unsexier name.
So, if you start flirting with a straight guy, it will be best to collect cues as to what that guy likes so you can take the conversation into that direction.