When my cousin John’s daughter was very small, like, maybe three years old, she would tell the best knock-knock jokes. I used to babysit her and her siblings when I was in my early twenties so this would be about twenty years ago. I found her jokes so surreally hilarious that I would retell them frequently, which is why I still remember them.
Mustard in the custard.
My all-time hands down favorite continues the tainted-nursery-foods theme, but with a darker twist:
Spiders in milk.
This joke’s genius (in case it’s not obvious) lies in the fact that the idea of spiders in milk is so utterly shudder-inducing. (You have to say the punchline slowly and in a whispery yet gleeful tone for the proper effect.)
You know Julia Kristeva’s thing about the abject and the skin on warm milk? Well, that’s only because she’d never thought of spiders in milk. Spiders in milk is a diabolical prospect. Just think of spideriness and milkiness conjoined and tell me you don’t recoil. It’s an unholy union. It’s what a witch would drink before bed. 
That being said, until this morning I had never empirically confirmed that spiders in milk are actually creepy in reality as well as notionally.
Until this morning.
This morning, I took a mug from the cupboard.
I poured milk in it for my morning coffee.
And as I poured the milk a tiny spider skittered up out of it causing a strange noise to emanate from me eeeeeuuuuoooohhhhhaaahhhhhhhit’s a spider it’s a spider (in disgust) it’s a spider in milk (with dawning realization) spiders in milk … spiders in milk??? (and finally with an odd jubilation) spider’s in milk!!!
SPIDER’S IN MILK!!!!
 Cf. Crazy Ex-Girlfriend: “is it possessive ‘Spider’s’ or plural ‘Spiders’’?”
 She’d have to open her throat wide to get the spiders down, the way that Andrea says you have to when you drink pulpy orange juice in Starring Sally J. Freedman As Herself