It is the bandPrimus' slogan, meaning that you would say it if you really like primus. they got sick of the slogan after awhile but some people still say it because it's a great slogan, so if you see someone post a comment on a youtube video of primus and they say primus sucks give them an E-high five.
WRONG!
Fan: Primus sucks!
noob primus fan: dood primus doesnt suck fuck u