The term used in the gay community to describe a boy or man (often teenage or young adult) who dresses up as a girl, frequently appearing in public or posting online pictures of themselves dressed as a female.
Unlike real transsexuals, and unlike drag queens, buffalos do not dress up for comic effect or from real belief they should be a girl. The exact reason varies with the person, but it tends to be from a mistaken belief that to be beautiful one must emulate "classical beauty", i.e. femininity.
Buffalos therefore often have deep self-image issues which manifest as dressing as something "beautiful", often coupled with a facade of overconfidence or swagger. Buffalos crave the attention given to their new "beautiful" appearance.
The term "buffalo"is derived from "Buffalo Bill", the tortured character in the movie "The Silence of the Lambs" who famously dresses up as a woman while saying "would you do me? I'd do me".
"I went to that new gay club and it was full of buffalos!"