What are some examples of awkward sounding but grammatically correct sentences?

"Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo."

That that exists exists in that that that that exists exists in.

Jim opens a cafe selling fish and chips. He has a sign made. It arrives and it says "fishandchips". So he rings up the sign company and says:

You need to put more space between "fish" and "and" and "and" and "chips"

James while John had had had had had had had had had had had a better effect on the teacher.

As far as awkward-sounding is concerned, I submit there are few sentences spoken in English that sound more awkward than:

Ed had edited it.

This is very hard to say in the rapid flow of conversation, and results in a sound something like:

Edədedədədit.

Try it for yourself, speaking quickly, and you'll see what I mean.

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