A Hot Tub Time Machine reference in Avengers: Endgame creates something of a paradox concerning actor Sebastian Stan. The original Hot Tub Time Machine is a rowdy, R-rated comedy starring John Cusack, Craig Robinson and Rob Corddry, that sees a group of friends transported back to the 1980s after a heavy night drinking in a hot tub. The film had a lot of fun with its silly premise and has since become a cult comedy. It also threw in an appearance from Crispin Glover as a nod to Back To The Future fans.
The movie's success led, unfortunately, to Hot Tub Time Machine 2. This entry was produced on a lower budget and Cusack opted out of returning, and was replaced by a new character played by Adam Scott. The sequel was a box-office dud that scored roundly negative reviews, where it was labeled a crass and mean-spirited follow-up to the first movie. Despite the ending setting up another adventure, another sequel looks unlikely.
One actor who didn't return for the sequel was Sebastian Stan, who played douchy bully Blaine in the first Hot Tub Time Machine. Stan is now best known for playing Bucky Barnes - AKA The Winter Soldier - in the MCU, having played the role since 2011's Captain America: The First Avenger. Bucky seemingly perished - alongside half the universe - at the end of Avengers: Infinity War, but he later returned in Endgame. The latter movie also referenced Hot Tub Time Machine, which creates an interesting paradox.
Click here to watch 15 Meta Movie Moments You Completely Missed on YouTube.
During a scene in Avengers: Endgame where Hulk explains how time travel works to Rhodey and Scott, they cite other films like Back To The Future and The Terminator for their understanding of the concept. Hot Tub Time Machine is also brought up, which of course featured Sebastian Stan in a key role. This suggests the actor himself exists in the MCU and is the exact doppelganger of Bucky. For such a pop culture savvy group as the Avengers that makes it a little strange nobody has noticed this, but who knows, maybe Stan has already played Bucky in a Winter Soldier biopic in the MCU.
Avengers: Endgame's nod to Hot Tub Time Machine isn't the first time the MCU has brought up other work from actors who've appeared in their movies. Star Wars, for example, has been brought up a few times and Natalie Portman and Samuel L. Jackson have played major roles in both franchises. It would be intriguing to see the MCU brooch this topic one day, but it's probably best not to pull on that logical thread. Sebastian Stan will next return as Bucky for Disney+ series The Falcon And The Winter Soldier.