I've made a semi-official profile on determining if someone is a closeted homo or is infected with the gay:

1. Avatarfags as a specific girl or consistently posts girls that are anime.
2. Avatarfags as a specific cute boy or consistently posts boys that are anime and cute - posting manly men (even if anime) isn't necessarily a sign of the gay unless it's a guy with minimal clothing.
3. Consistently shows up in gay threads instead of just hiding/filtering them like a good straight.
4. Posts pics of himself on a 99.9% male board with over half of the population being bisexual.
5. Constantly denies being gay while consistently showing up in gay threads.
6. Constantly finds himself wrapped up in gay drama whilst denying being gay - it could be said that the gays are following him around, but that doesn't really happen unless number two happens.
7. Attention whores on a 99% male board.
8. Likes futa/dickgirls.
9. Admits to liking traps for their femininity.
10. Has admitted to having at least one IRL gay experience.
11. Shows up in gay threads to "derail" them into an attention whore thread for himself.
12. Threads become gay drama threads as soon as he appears.
13. Stutter-types on an imageboard.
14. Gets flustered easily.
15. Adds hearts (<3) or text-based emojis in their comments (/ᐠ｡ꞈ｡ᐟ\, (´・ω ・｀) )
16. Has admitted to visiting /lgbt/ at least once.

If you show even a quarter of the signs on here, you have the gay. See PD for treatment.