be disappointing be unproductive blow up break break down burn out cave in collapse come apart come short come to naught come to nothing come unstuck conk out crumble decline die die away die out disintegrate droop drop explode fade fail fail miserably faint fall down fall flat fall short fall through fizz out fizzle flag flame out get bogged down get hung up get mired get nowhere give out give way go downhill go out go phut go soft go to pieces go wrong hang fire hang up hit the skids languish lie fallow misfire not hack it not make it peg out peter out pine poop out sink turn sour weaken wear away wear thin wilt yield