To "gargle horse loads" is to have something be thoroughly terrible. Anything can commit the act of gargling horse loads. Such as a person, an object, an event, etc, etc... It is never a good thing and can be used an unlimited number of times.
"Dude, the party gargle horse loads!"
"Dude, your car gargles horse loads!"
"Dude, I bet that chick gargles horse loads in bed."
"Dude, that Urban Dictionary entrance about gargling horse loads gargled horse loads."