Victoria Gannon charts the plaid fad:
In the 1970s, plaid became a site of negotiation, enabling a partial collapse of a false dichotomy. It was during this period that many gay men adopted a hyper-masculine look, claiming traditionally heterosexual symbols and asserting their own manliness. “[G]ay men looked towards traditional images of rugged masculinity, such as the cowboy or lumberjack,” writes Shaun Cole in Don We Now Our Gay Apparel, his history of gay men’s dress in the twentieth century. “All these clothes had a clear meaning in the wider American culture: toughness, virility, aggression, strength, potency.” Two supposed polaritieshomosexuality and heteronormative masculinityunite in one fashion statement; both identities are destabilized in the process. Plaid continues to be prominent in gay male culture, having been coined “bear chic” in a 2009 article in the Advocate.
Either that or we got it from the lesbians. I was wearing plaid back when I was a twink. At the very least, it's practical.