Acronym for Mount
Taint Bike, which is old slang for a Mountain Bike. Riding a bicycle on rough terrain causes repeated trauma between the rider'
s legs; in male cycling enthusiasts, this often leads to irritation and swelling of the prostate. This would result in a characteristically swollen perineum (a "mount
taint"), the external manifestation of both
local trauma and the enlarged prostate beneath.
With the increased popularity of padded bicycling shorts, the "mount
taint" phenomenon has decreased in frequency (though by no means disappeared), and many cyclists nowadays are unaware of the origin of the term MTB, believing instead in a folk etymology that describes it as a nonsensical acronym of *"mountain bike" ("MounTain Bike"?).
Albert: Hey Bob, what's up? You
don't look so good!
Bob: No kidding! I had to see my proctologist last week... now I get why they are called MTBs!
Albert: Ow.