Humbug. A fish, not a bug.
Grape drupe. Grapes are berries, peaches are drupes, but a grape drupe is a snail.
Two Spanish ones:
Hormigas león. Ant lions aren’t ants, they are predators of ants, but the syntax sounds like they’re a lion kind of ants. I checked Wiktionary, which has it pluralized on “hormiga”.
Playero pihuihuí (some bird in Charadriiformes). I think “pihuihuí” sounds funny.
Mmm, that’s becaue it’s Catalan, not French. It means …‘whatever’.
Sounds like somebody got bored, maybe? 
I like the Chriacus.
Macaroni Penguin, Oilbird
A few of my faves:
Smew ( a bird)
Rustic (The least rustic looking butterfly- kinda ironic)
Chicken turtle ( A turtle)
Sarcastic fringehead ( A fish)
Aha ha ( Just google it)
EDIT: Aha ha is a wasp.
Monoculus monstrosus (also known as Octeospermum monstrosum) has always felt absurdly dramatic for a random weedy daisy. Monopsis debilis - ‘Devil Oneeye’ on iNat - is about as intimidating, and on an even smaller weed.
Octopus Stinkhorn
Dog Vomit Slime Mold
I was once told that Calycanthus floridus is sometimes called “scrotbush” due to the suspicious looking fruit. This was by someone who grew up in very rural Appalachia, so I assume this is such a niche regionalism that I can’t find any record of it online, or he just made it up.
Lesser Broomrape
Bastard Toadflax
Broomrape! Wikipedia tells me it’s also called ‘Hellroot’. 100% accurate
Bryophytes are great for this:
Anomalous Flapwort
Handsome Woollywort
But so are fungi:
Eastern American Alder Tongue Gall Fungus
Powdery Kidney Lichen
Stinking Orange Oyster
Bark Barnacles
“debilis” is Latin for “weak,” not for “devil.”
Difficult sea cucumber (Holothuria difficilis). Probably named for taxonomic difficulty, like the confused flour beetle.
Pumpkinseed, A fish.
When one knows very little latin it sounds scary. And I don’t know why that’s the common name it has on iNat, but it is!
boops boops
sarcastic fringehead
pleasing fungus beetle
fried egg jellyfish
humuhumunukunukuāpuaʻa
Gosh what a name!
GANDALFUS (crab genus)
I think it’s Hawaiian.