Primus is one of my 3 favorite bands... The Bass Player/Singer/Founder is a God named Les Claypool..... Primus Sucks is from a live album they did called Suck On This, on which, after the song Jellikit, Les says.....
"Thanks alot.. We're Primus, We Suck..."
And it just stuck... People yell out "Primus Sucks" as a tribute to how awesome the band is.... I have several T-shirts that have this on it....