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1.
getting up (relatively)early, rushing to the local McDonalds, only to discover you missed the breakfast mark by .0005 of a second.
Guy that got dragged out of bed: Dude, that was such a McLetdown!
Guy that suggested it: sorry, man.
by bob_of_bobs April 14, 2006
 
2.
When you go out of your way to get a MsDonalds Hot Fudge Sundae, only to discover that the machine is broken.
McDonalds Dude: Can I take your order?
Jeff: Can I have a hot fudge sundae please?
McDonalds Dude: No, the machine is broken.
Jeff: Awwwwwwwwwwwwwwwwwww!!!
Heartless Friend: Hahahaa, what a McLetdown.
by The real D-Man April 30, 2006
 
3.
(noun) an event that may cause one party a source of entertainment due to the frustration of another party specifically-wanting something (food or toy) from McDonalds.

E.g. Keito was pissed off because they no longer served hashbrowns when she arrived at McDonalds about half a second too late! This McLetdown only provided amusement to her sibling who drove her there.
by fitchickxina April 30, 2006
 
4.
Looking forward to a McDonalds icecream all day only to find when you get there that the icecream machine isn't working/is empty/is being cleaned (although THAT one doesnt happen much) so you miss out.
Customer: Can I have a 50 cent cone please?
McDonalds Chick: Sorry, the machine isn't turned on.
Customer: @#%$! That is such a McLetdown!
by Icecream Fan April 30, 2006
 
5.
The feeling of dissapointment one gets when they're with MC HAMMER and he won't let said person touch anything.
*Vannila Ice hangin' out with MC Hammer, Ice goes to grab some chips*

MC Hammer: naananana, nana, CAN'T TOUCH THIS!!
Vannila Ice: damn bro.. What MC Let-Down..
Random Civilian: chronic fail man..
by Barca,A January 31, 2010
 
6.
Having a craving for McDonalds, going to a McDonalds, buying a hamburger, and tasting it.
McLetdown
Human#1: Dude, I had a McDonalds Humburger yesterday
Human#2: *shakes head* McLetdown!!
by SH8aP May 01, 2006
 
7.
Discovering, and worse swallowing, and worse yet wretching up blood and cutting my lip, as a result of foreign objects(sharp plastic) in my and my son's McDonalds sundaes. The first sundaes were watery so we returned them but got new ones with objects inside... I had nuts and my son didn't. I wish I hadn't asked for nuts and I wish I hadn't been served such a McLetdown!
McLetdown - Be glad that the sundae machine was down and you weren't served a sundae like mine because I had a scary McLetdown!
by McLetdowned Customer March 19, 2008