Did Pumpkin and Honey Bunny from Pulp Fiction appear in another movie? Because I believe I've seen some coffee addicted idiots looking similar to them in some another movie. Am I confusing them with someone else?
No, neither character appeared in another film.
A check of IMDb and a Google search show that while Tim Roth has appeared in three Quentin Tarantino projects (Pulp Fiction, Reservoir Dogs and The Hateful 8) Amanda Plummer (Honey Bunny) has only appeared in Pulp Fiction. Additionally neither character seems to have been used elsewhere by Tarantino who owns part of the rights to the film and would have to be credited and compensated for the use of his characters in anything other than a satire or parody of the role.
You may have conflated the details of another film (such as Natural Born Killers) with this one, although the characters were not the same. Or perhaps you have saw a parody of the film on a sketch comedy show. Either way, Amanda Plummer (so far) has appeared as Honey Bunny in a single Quentin Tarantino project and no parodies of the original film.