The music playing in the background of the tattoo parlor scene is one of the songs performed by The Vulture's band in The Oolong Slayer (2015).
When Jake and Charles are having a drink at Shaw's, Charles is wearing the t-shirt that he borrowed from the Texas Boyles in 99 (2017).
This aired in Jan 2020 and totally predicted the great toilet paper shortage of March 2020.
Jake (reading tattoos off of Pimento): "Okay this one says 'Buy toilet paper', in a truly gigantic font.
I hate to think of the horrific event that lead to a reminder of this size."
Jim Rash starred in Community (2009), which, like this episode, would often parody and pastiche well known movies and tropes. Furthermore, both Jason Mantzoukas (Pimento) and Joe Lo Truglio (Boyle) had guest roles on Community: Mantzoukas played the director of the play Chang starred in (Queer Studies & Advanced Waxing (2015)) and Lo Truglio played Mark, the lawyer friend of Jeff who informed him about his disbarring, in two episodes.
The window ledge that Pimento, Jake, and Charles end up on is the same window ledge that Jake and Terry stood on in Terry Kitties (2016).