Are you gay if you stick things in your anus?

No. You are gay if and only if all or most of your sexual experiences and fantasies involve another person of the same sex as you.

Increasing numbers of straight men are discovering that anal stimulation can be sexually arousing. There are basically a couple of reasons for this. First, men have a gland called the prostate in the area between the anus and the penis. Stimulating this organ can trigger an erection. Second, the whole area between your legs is filled with nerve endings that feel good when they're stimulated.