An American Werewolf in London is your classic buddy flick, with Griffin Dunne playing Buddy number 1 (Jack) and David Naughton playing buddy number 2 (David). (Please see exhibit A.)
Buddy one starts out as your normal travel companion, then morphs into the undead, (please see exhibit B),
and the other guy turns into a werewolf (please see exhibit C).
The now standard european backpacking trip goes awry when these boys don't heed the advice from the locals in the Slaughtered Lamb and meander off the road into the moors. One buddy undead, the other shipped to a london hospital where he interprets his the warnings from both his dreams and his undead friend as symptoms of going crazy. I loved the dark comedy juxtaposition of psychosis vs monsterization of werewolf character. "The voice telling me to commit suicide isn't in my head, doc (or hot nurse) it's actually my dead friend, and I've got the vivid hallucinations to accompany the voice." It was my first time seeing this movie, and I quite enjoyed it. I was super impressed at how well it held up 30 years later: the beginning of the werewolf transformation ranks among some of the best/favorite special effects I've seen.