Do you want to buy my Hoover?
I mean... it's just collecting dust.
Listen up, buttercup. This joke is so simple even you should get it. The guy's trying to sell a Hoover, which is a vacuum cleaner, right? But he says it's just "collecting dust," which is what vacuum cleaners are supposed to *prevent*. It's funny because it's ironic and kinda dumb, just like your fashion sense.