It's one of mine as well.
I had to do a group presentation on it- my classmates thought I was insane when we alien-abducted them. The talking plungers confused them also.
I'm not really a fan, but I've read a majority of em.
I don't think the shirt is really referencing Vonnegut...overanalyzing is a pet peeve of mine. The title's relevant only to the design, not the literature.
I haven't read Slaughterhouse-five yet, though.
I've only read some of his short stories..