I usually use these to describe the equipment I use at work (which half the time either screws up or just doesn't work at all). Note that there is an escalation, depending on how bad it's malfunctioning...

POC - piece of crap
DPOC - d*** piece of crap
POS - piece of $hit
FPOS - f***ing piece of $hit
MFPOS - you can imagine
GDMFPOS - well, you get the idea...this is the worst designation, at least that I can think of. If anyone has one any worse than this, I'd love to hear it....