The commentary-PDF suggests that one of the reasons Karkat is always so angry is that his themesong plays everywhere he goes.
"heya kk, how'2 iit going"
"WHAT?"
"ii said hello karkat, are you deaf or some2hiing?"
"I CAN'T HEAR YOU OVER THIS DAMN THEME MUSIC!"
"what."
"ARGH, FUCK IT!"