"Let me stop" is one of the few actual phrases on Urban Dictionary that is slang. Though the exact origin of the phrase is unknown, like with many, it is often used here in New York.
It is usually used by one who is doing OR saying something that can be considered:
Overdoing it
Ridiculous
or perhaps going to far (as a previous definition suggested).
Tyrone: "That girl you talk to looks good, I should holla at her."
Shaniqua: "What? Did you see that girl's weave?"
Tyrone: "That's her realhair, ain't it?"
Shaniqua: "Please, that bitch is bald. And her hair, that shit is fake. Nah, let me stop."
Shaniqua realizes that she's saying too much, whether funny or not, and because of this... she uses the phrase "Let me stop" at the end of her statement. Shaniqua needs to stop getting out of line.
Joe: "Hey Bryant, fresh cakes! Michael is doing the fappy face right behind you!"
Bryant; "Is that right Joseph? Then I guess you should... let me stop in my tracks! *thrusts arm back and hits Michael in the face*
Michael: Not now Bryant...
You use this phrase when someone repeats a story over and over or if a person is just spouting bull shit. Instead of saying "You're full of it.", you can say (in a sarcastic tone) "Well....stop the world and let me off".
It's also an appropriate response to a big surprise.
When some resigns or retires from a job, they are on "eternity leave". This can also refer to someone who has passed away, especially someone who worked somewhere for a long time, retired/resigned, then passed away later.
Oh I'm sorry, you didn't know that Kelly is on eternity leave? She resigned and moved to Hawaii!
With regrets I would like to inform you that my boss is officially on eternity leave. I will never see or hear them again. Ever.
The hypothetical man (often a sinistercharacter who decided not to go to boot camp) that is doing your girlfriend/wife while you are on deployment overseas.
Ain't no use in goin home,
Jody's got your girl and gone.
Ain't no use in goin back,
Jody's got your Cadillac,
Ain't no use in feeling blue,
Jody's took your checkbook too.