Where does that phrase a deco at this come from?

The phrase "a deco at this" is not a common or widely recognized phrase in English. It's possible that:

* It's a misheard phrase: You might have misheard a similar-sounding phrase. Can you provide more context or information about where you heard it?

* It's a regional expression: Perhaps it's a slang term or idiom used in a specific region or community.

* It's a made-up phrase: It's possible that the phrase was invented or created by someone for a specific purpose.

If you can provide more context, I might be able to help you figure out where the phrase comes from.