n. An undergarment designed to give a man a slimmer appearance, particularly at the waist.
It's only since men have become increasingly visible half-naked in underwear commercials, horny clothing line ads, firefighter calendars, and the lot that men have begun to face mounting pressure to conform to exacting standards of physical appeal.

Thus, we've witnessed the growth of shapewear for men, including the mirdle (a girdle for men), over the past decade.
—Craig Takeuchi, “What happens when men try on shapewear,” The Georgia Straight, August 15, 2014
Precision pouch. The waist eliminator. The Saxx package separator. Ab control tank. This is the language of selling body-shaping underwear to men.

What you must not do is call them girdles (or the more gender-specific mirdles), supportwear or even shapewear.
—Fiona Smith, “What’s under your colleague’s suit?,” Australian Financial Review, July 04, 2014
Known as "mirdles" and engineered to taper even the most bloated of blokes, corsets for men are hitting the market faster than you can say love handle.
—Rosemarie Lentini, “Corsets for men, known as mirdles, reduce a man's waistline by up to 5cm,” The Daily Telegraph (Sydney, Australia), January 04, 2010
2007 (earliest)
I see, I thought it had to do with the actual construction of the waistband in the pants, like a mirdle (man's girdle).
—farfisa23, “Waist suppression, please explain…” (reply), Styleforum, July 12, 2007