For me, the cheap yellow swill that most people have covered above was bad, but not memorably bad. Memorably bad would have to go to Brau Brothers Scotch Ale. I hate to rag on a local brewery, but these guys must use about 50% peat smoked malt in that beer, rendering it completely undrinkable, IMO. I couldn't even finish the tasting sample I was given at a beer festival last summer. I tried to give a smile to the rep who poured my sample after I took swig, but it was difficult to hide the fact that it was just awful.