Thingummyjig... Whatsisname...

You are speaking Polish.
Perhaps you are Polish.
Perhaps you are fluent.

... But you just can't think of a particular word or name.

Suddenly your mind goes blank.
It happens to us all sometimes.

What word (like the English 'thingammybob) do you use?

sometimes badziewko works for thingiemagig even though badziew really usually means some cheap piece of crap

There is no such word. Maybe polish is so simple there is no way to forget anything ;-)

So could I get away with using any random word?
I don't get to use the word 'Bakłażan' enough, and if I want someone to pass me the brush and I momentarily forget 'miotła'...