Some of the extremely extreme death metal and grind bands (plus attendent spin offs like gore-grind etc etc) 'sing' about pretty 'what-the-fuck' gruesome and wantonly offensive stuff, albeit in a fairly cartoony way.
I can take a joke... but certain really aggressive 'screamo' stuff leaves me cold. Mix that migraine inducing sound with nonstop lyrics about killing people.... and my tolerance level is blown to hell.