Kindergarten Cop (1990)

Arnold is a cop who has gone undercover because some kid's stepdad is in the mob. (Either that or the kid's real dad is a witness on the run from the mob.) Implausibly, Arnold poses as a kindergarten teacher—and hard though he may be on the beat, he just is not cut out for dealing with adorable children! (Then he is.) I believe he gets shot in a shower but is OK.*

Why do people say Schwarzenegger can't act?

* Oh, and of course, "It's not a tumor!" But that was in the trailer and therefore doesn't count.