The reverse of one-upmanship, one-lowmanship is practice of successively outdoing a competitor by spending less, having less, or doing less. Originated on Offbeat Bride to describe the indie-er than thou, DIY-er than thou, lower-budget than thou attitude that nontraditional brides can sometimes slip into.
Then she said, "You call THAT a low budget wedding? My wedding budget was $15, and we managed to feed 115 guests." It was totally one-lowmanship.