abrasive, aggravate, annoy, badger, bedevil, beset, bother, chafe, conundrum, cumbersome, defect, difficulty, disagreeable, dysfunctional, exasperate, flaw, hamper, hassle, hinder, impede, impediment, importune, incessant, invalidate, irksome, irrelevant, irreparable, irresponsible, irrevocable, irritate, irritating, irritation, lack, nettle, niggling, nuisance, pernickety, pitfall, plague, predicament, rankle, riddled, untoward, vexatious