I have just seen in the youtube comments section of a video I was looking at:
"Du hast einen an der Waffel, das ist alles!"
What does this mean exactly?
"Waffel" is a pastry, but it was also an old word for mouth or head that isn't used any more except in some idioms.
The english word "to waffle" (to ramble, to prate) is related.
"Du hast einen an der Waffel" means there's something wrong with your head, you're a lunatic. It's not really clear what "einen" refers to in this idiom, presumably some kind of damage.
"Du kriegst gleich einen auf die Waffel" would mean you're on the verge of getting hit on the head or the mouth.
"Du hast einen an der Waffel, das ist alles!"
means "You're a lunatic, that is the end of it."
Goes without saying that it is rude to the max, even for a Youtube comment.
Einen an der Waffel haben is a sloppy phrase denoting intellectual deficiencies in the same category as:
Additional material found at Rolf-Bernhard Essig on SWR or Gesellschaft für deutsche Sprache. Due to these numerous examples (there seems to be a pressing need to state that meaning) there seems not much benefit of mentioning that Waffel refers to mouth, which is considered as outlet from the special brain; but it may assist in remembering the meaning.