2 letters

various initialisms
(bs, sf, hp, bb, cf, ism)

note: there are more detailed lists on wikipedia,
but these are mine:

bs
bible study, bullshit, bernie sanders, behavioral science, bachelor of science, buy/sell, balance sheet, bahamas, programming language, backspace, bright star, big sister, blocked shot

sf
san francisco, suck fuck, strawberry fields, science fiction, speculative fiction, st. francis, society of friends, street fighter, small forward, sacrifice fly, semi-finals, sasha fierce, sinn fein, stormfront, special forces, state farm, six flags, swedish fish.

hp
honey pie, harry potter, hewlett packard, higher power, hunters point, howard phillips (lovecraft), horsepower, hydrogen peroxide, health professional, hollow point, huffington post

bb
bodybuilding, gun, bungalow bill, bibi (netanyahu), bela bartok, bb king, big ben, busy beaver, battleship, bed and breakfast, barbara bush, benazir bhutto, brigitte bardot, best buy, brooks brothers, black bird, boston brahmin, bounce back, big brother

cf
cystic fibrosis, clinton foundation, chaplain to the forces, cabin fever, carbon fiber, consolidated freightways, californium

a few extras:

ism
international soccer match, insanely stupid mistake, ignorant stupid moron, intelligent smart mind

queer innuendo
cape horn, scuse me while i kiss the sky, homeowners
  (gay porn, kiss this guy, homo)
 gay candy: m and m's, twix, her-she's
 phallic beverages: gatorade and coke (G, cock)
      and, of course, 7-up
how long till we get there?  I'm hungry!