LETTER DROP parsed into LET TER DROP. PORTRAIT PAIN made me chuckle-cringe, imagining a model developing a cramp, and the painter pleading for him/her to hold the pose just a few more minutes. (I have a weird phobia of being asked to sit for a portrait, in a fixed position for a long period of time. There's probably a term for it — fixaphobia?)
I had a good laugh at PRAIRIE OYS, people in wagon trains kvetching about the rough rides. I didn't know what a PRAIRIE OYSTER was, though, which took away from the amusement. Apparently, it's a hangover "cure" consisting of raw egg, Worcestershire, hot sauce, salt, and pepper.
I'd rather have the hangover.
LETTER DROP does have dictionary support, but is the term used these days? Hard for me to say since I rarely go to the post office. I think I've seen slots before, but I always thought they were "mail drops."
No long bonuses in the grid, but CHIMERA, ERNESTO, POISONS, and PLODDED are all pretty good. I especially liked CHIMERA, as it has so many interesting definitions: the Greek fire-breathing monster, a wished-for thing impossible to achieve, and a biological organism with a mixture of genetic tissues. Great word.
Some crossword glue holding everything together. But considering there are six themers, to keep it to the minor evils of LAN (local area network), UPSY (can only clue it one way), HST, TSP, DES, and AM SO isn't bad at all. PREXY isn't something I've ever heard in real life, but it does have dictionary support. Perhaps it's a term used more by a different generation?
None of the themers made me out-and-out laugh, so I might have liked fewer examples. That would have allowed for more sizzling bonus fill like CHIMERA worked in for good measure, plus fewer short, gluey bits.
ADDED NOTE: Reader Deb Gordon points out that PRAIRIE OYSTERS are also slang for ... ahem ... bull testicles. OYS indeed!