Hot Tub Time Machine—the title itself speaks volumes. But with time travel guaranteed from the outset, the movie's jokes aren't just about the past, they're about what you're supposed to do when you get there.
Hot Tub Time Machine is rated R, it's very funny, and it once again features the same group of characters, although they're rendered even more sketchily.
While the movie's keenly aware of the present moment in which it exists, it's also very knowing of its place in the lineage of time travel cinema. The generic standby of the "old time travel guy"—the obscurely wise old man who understands the secrets of time—is present and accounted for (he's a familiar face) and he's treated as that stock character throughout the movie. Another cameo comes from a well-known time travel movie veteran who serves as a bell-hop for the resort at which the titular tub is located.
The main characters have seen Back to the Future and compare their experience to Marty's.
What all of this amounts to is establishing characters whose experiences are familiar to the audience. Their lives aren't always glamorous and their jokes aren't always sophisticated. They have ordinary jobs and ordinary problems. And when they time travel back to the 1980s, they don't get mired in metaphysics. They just set out to have fun (albeit the exact fun they had the first time around.)
