Ken Callicott messaged me on Facebook to say that he’d come across the men’s underwear term T-bar (or t-bar), which was new to him (and to me), though the metaphor (as in t-shirt, based on the appearance of the letter T) isn’t hard to puzzle out.
The source was a news story on neighborhood complaint about a (men’s) stripper bar:
The backlash from neighbors isn’t the content of the shows, choreographed dance routines performed by men who strip down to their T-bars (which provide more coverage than a G-string), but with the type of clientele those shows might attract and possible security and noise issues, said Ronni Kotwicka, president of the Palo Verde [AZ] Neighborhood Association.
An illustration: a Men’s Brazil T-bar thong swimwear/underwear item offered on eBay:
Some sites describe T-bar as simply slang for thong, a label that can refer to underwear from the very skimpy (just up from a G-string) to something many people would call a brief. Most purveyers of men’s underwear seem not to use the descriptor T-bar at all, preferring simply thong. But a few sites, like eBay, refer to T-bar thongs (as above); it’s not clear whether this is to be understood as picking out a type of thong or as referring (redundantly) to thongs in general.
Women’s T-bars are available as well, often in flamboyant styles (with rhinestones, for example). And that brings us to The T Bar Boulder in Boulder CO:
This hot lingerie store is owned by Debra Caplin. It offers a line of under-garments and swimwear from the classic to the subtle sexy look for women, men, and even kids. The store stocks thongs, g-strings, butt shorts and anything else you can think of that goes under the lingerie category! (link)
Here, T-bar looks like a cover term for all sorts of abbreviated underwear.
So usage appears to be in flux.