"you are about intelligent enough to pick up yellow snow thinking it's gelato" "all your "perfume" does is make you smell like a cow shit in a rosebush"
"Woodstain spilled on carpet stinking up the room" and one of my favorite evergreens: "Bread can at least mold, what do you bring to the table?"
"I know there are many in need of more brain, but you weren't obligated to give yours away entirely." "I wish you good health and longevity. When I die, I want you as far from me as possible for as long as I can get." "If I enumerated your faults I'd die from lack of breath, and my ghost can surely be put to better work than an eternity spent trying to finish the list." "All of you can relax. None of your lives were worth the expense of poison." While it's less good for direct mining, I feel like this should be shared anyway, if only for the opening: "Ingrates, simpletons, and leeches" is one hell of a way to kick off a general address. (I also just realized I stole my second one here from that sketch, at least partially.)
"Your mother doesn't know enough to be ashamed of you, poor woman. I don't blame her, you were the very best she could produce. It's not her fault you've all been working with substandard materials for the past fifty years."
Perhaps too juvenile, but: giving someone an uncomfortably long stare before comparing them in thorough detail to a reindeer's junk.
I'm very fond of XKCD's "gosh-darned cunt" and have every intention of having an unusually stressed Zahhak say it in a fanfic. Some of my fave books have some good ones, too. My favourite is "if brains were bread, you'd have starved to death before you were born!" Or: -Mattimeo, Brian Jacques -Path of the Perambulator, Alan Dean Foster
Oh, oh, one from Goblins: "Your existence demonstrates a flesh-to-futility ratio that is mathematically staggering!" And a long string from Something Positive (tw: implications of physical/sexual abuse).
One from a fanfic; "There had definitely been alcohol involved before and after his mother popped him out, and perhaps during."
Not sweary exactly, but my (Christian—Episcopalian but culturally pretty Catholic) mom is fond of “Jesus, Mary, and good Saint Joseph!” as an exclamation when just “Jesus” isn’t enough.