This has to be about really aggressive vindication. The line "I have something against you" could be a) I have been mistreated and I have a grudge against you now, b) I have evidence of your deceitful, miserable, etc. ways and I could blackmail and assault your public image or c) You have debased me and I want to debase you in revenge, maybe physically, which the line "I am one happy prick" suggests.
This has to be about really aggressive vindication. The line "I have something against you" could be a) I have been mistreated and I have a grudge against you now, b) I have evidence of your deceitful, miserable, etc. ways and I could blackmail and assault your public image or c) You have debased me and I want to debase you in revenge, maybe physically, which the line "I am one happy prick" suggests.