I was more horrified that the whole theater spontaneously found it hilarious I guess?
I think death, if treated cartoonily (or if it's especially stupid) can be funny. I can't think of an instance in which someone's brains are accidentally blown out all over the rear windshield of a car would ever be funny.
Be thankful you didn't see The Devil's Rejects at theaters. From accounts I've heard, teenagers were cheering on the
rapist serial killers. And once I read the internet signature "Captain Spaulding is my hero."

And they weren't talking about the Groucho Marx one.

I'll tell you a Tarantino moment whose audience reaction sickened me: in Kill Bill Volume One, when it's revealed that a comatose Uma Thurman's body has been pimped out for comatose rape. People just thought it was just hysterical when the dude held up that jar of Vaseline while explaining to the would-be rapist how he'd need to lube up her dry vagina. "Sexually violating coma patients, LOL."
As for the Pulp Fiction scene you object to: I find the shotgun scene funny because the actual act is quick & it's played out like a comedy of errors. I think part of the humor is their amorality and their panic is purely the inconvenience of the situation (it is, in a very black way, "situational comedy"). What I
don't find so funny is a few minutes later when Tarantino delivers that endless self-written monologue about "dead nigger storage". That gives me the creeps way more than the splatter.
(Well, if anything, this post should confirm my anti-rape credentials.)