Flexing rhymes with:
perplexing, annexing, perplexing, vexing, affixing, annexing, boxing, coaxing, faxing, fixing, indexing, intermixing, mixing, outfoxing, perplexing, relaxing, taxing, vexing, waxing, xeroxing
Flexing sounds like:
falcons, feliciano's, felkins, filkins, flagging, flaking, flashguns, flashing, fleecing, flicking, flocking, flogging, flushing, foolishness, fulgencio