Family Guy references South Park?

[.TowlieCartman.]

Season 14 Episode 05 peter has a box of pornos, one of them is Backdoor Sluts 4. I wonder if Seth was referencing South Park!

[Big-Will]

Yes, from what I've read elsewhere.

Peter is looking through his old collection of porn and finds one called Back Door Sluts 4, directly ripping off the title of the movie in SP S06E13 "The Return of the Fellowship of the Ring to the Two Towers" which was Back Door Sluts 9. Then he says, "Eeh I never saw one through three so I wouldn't know what's going on." which is almost exactly what Butters says about Fisting Firemen 9 in S05E14 "Butters' Very Own Episode."

Indeed, there are two SP references here.

"Peter, Chris & Brian" 14x05 (11/09/15)
Peter: Back-Door Sluts 4. Eh, I haven't seen the first three.

"Butters' Very Own Episode" 05x14 (2001)
Butters: Fisting Firemen 9. I've never seen 1 through 8
"The Return of the Fellowship of the Ring to the Two Towers" 06x13 (2002)
Randy: I'm a...fraid it was... Back Door Sluts 9.

They waited 13 years to make SP references, lol.
Also interesting that the episode and season numbers are switched.
SP 05x14
FG 14x05

But both shows references 1990s porn movies which become series, like the Pussyman movies, which made it up to Pussyman 17.