The movie that Lance is watching when Vincent arrives with overdosed Mia is the Three Stooges short, Brideless Groom.
Quentin Tarantino is an avid Three Stooges fan, but couldn't get the rights from Comedy III to show them in the movie. So while a Three Stooges film appears on screen ("Brideless Groom" is public domain),
The Three Stooges themselves do not.
Emil Sitka, the frequent Three Stooges co-star who does appear on screen, is credited as "Hold hands you lovebirds".