Two key culprits - bucolic and sanguine.
Bucolic. This word purports to evoke benign, pastoral, even soothing settings. For me it's much too close to bubonic. When I picture a bucolic meadow, an image of undulating grasses kissed by a summer wind manifests...but the field is littered with bodies in various states of decay. Like this:

Sanguine. The problem with this word is its relation to sanguinary - one of my FAVORITE words. For any of you who don't know sanguine = enthusiastic, cheerful, optimistic, whereas a sanguinary event involves lots and lots of blood. Or better yet, if you've been exsanguinated you had a date with a vampire that went badly for you, but had a happily-sated nosferatu at evening's end.
Though sanguine has come to dominate the lexicon, sanguinary is the older word, from which sanguine derived. In the past the two words had a more direct affiliation, sanguine also meant a ruddy, flushed complexion (get it? from blood rushing to one's face....aha!) but as language is always evolving and words grow distant from their own origins, at some point the relation of these two drifted apart and now the two meanings have become oppositional.
I stand firmly in sanguinary's camp.
So for me a sanguine pastime equates to turning lazing laps in the pool at your Beverly Hills Estate...but the pool is filled with AB negative instead of water.

(Hmmm, I'm really not sure what to make of the fact that I actually had a successful hit upon Googling "pool filled with blood"...I guess their "Don't be evil" motto went out the window (or was defenestrated for any fellow word freaks out there).
If anyone else has a word they can't stomach, let me know. I'd love to hear your own word sound/meaning divergence quirks.