Sometimes when I'm alone at home I like to put on the SheFlogger's thong. It helps me feel special. Now I can get the same feeling on the mountain with the CAMP Alp 95, a butt-floss of a harness for low-angle alpine and adventure racing use.
The Alp 95 weighs in at 3.5oz, about as much as a locking carabiner. An upgraded version of CAMP's XLH 95, the Alp adds a tie-in point and an adjustable waist belt. There is a loop on each side if you want to add a 'biner to rack gear, but the Alp really shines underneath a pack. The Alp lived under my Mchale hip belt on Denali this year and was not even noticable, as long as you don't get the little pad behind the buckle underneath. And make sure the waist belt lies flat before putting your pack on.
I didn't spend much hang time in the Alp for obvious reasons, but properly adjusted it is comfortable enough. The leg loops run small, and that can present a sizing problem; measure your thighs first if you're ordering online, because you might have to move up a size. That will mean you'll have to crank the waist down all the way. I'd like to see the leg loops an inch or two bigger for each size. Other than that the Alp really cuts down on weight. You see a lot of climbers sporting pound-plus harnesses on routes like Denali's West Buttress and Rainier when the Alp would do just fine.