The act of engaging in anal sex with a dirty stinky homeless bum (with the bum being on the "receiving" end). The "slide" portion of the phrase refers to the lack of need for decent lube, since in all likelihood the hobo hasn't wiped his/her ass in several months. We recommend wearing condoms, since you don't want all that feces to get stuck inside your urethra.
As a special contingency for the distinguished gay man, if your partner has ever "released" on you during anal sex, you could really embarrass the piss out of him with this.
Even more disturbingly, you necrophiliacs out there probably find this very useful (think about it).
Girlfriend/Boyfriend give ya blue balls? No problem! Head out to the park and take the hobo slide!