Slang for words/names you can't remember

The grammar term for forgotten words and names is Proname. There are occasionally times when a speaker cannot or will not recall the proper name for something or someone and need a term or two to fill the gap.

To replace common nouns for things, you can use:

(singular)

what-cha-ma-call-it,
whatyoucallit
thingamajig, thingamabob
whatnot, whatsit, youknow
British: doo-dah, thingummуbob
American: doo-dad (for small things), doo-hickey.
whatyoucallem (plural)

You must, however, be more careful when talking about people. Again, it is grammatically expressed:

whatsizname, whatyoucallim (male, singular)
whatsername, whatyoucaller (female, singular)
whatstheir name, whatyoucallem (plural)

We can talk about Mr. How-d’you-do, Mrs. Whatsername and President Whatnot when you genuinely can’t remember the names of absent people. If is not polite to speak directly to someone this way; “Hey, you, whatsyourname?” is deliberately impolite. Some shy poeople use pronames in place of a taboo word: “He’s a wicked old so-and-so.”

Lewis Carroll in “The Hunting of the Snark” made humorous use of pronames.

“He would answer to ‘Hi!’ or to any loud cry
Such as ‘Fry me!’ or ‘Fritter my Wig!’
To ‘What-you-may-call-um!’
or ‘What-was-his-name!’
But especially to ‘Thing-um-a-jig!’ “

Sample sentences:

I broke the whatchamacallit off the car door.
I can’t unfasten the whatsit; will you try?
Have you got the doodad that goes with this?
Press this button and turn that doohickey to turn it on.
Her brother, whatisname, will be at the party.