Last night's ep

Saw last night's episode for the first time. Could someone explain where the line "Now that was a sticky situation." came from?

It came from the City on the Edge of Forever episode (Flashbacks). The boys kept bringing up their old adventures, but their memories were always wrong and ended with someone eating ice cream. Anyway, at the end of every flashback someone would always say, "Now that's what I call a sticky situation!". ------ Kyle: Dude! Check it out; they're still reading this! Cartman: Don't you God damn computer nerd hippies EVER get tired of this? Stan: If they did, they wouldn't be here. Kenny: [To readers] Mmph, mm mmph mm mmhr mph? Stan, Kyle, Cartman: Gross!