Where do you hang out?

[El Nib]

[Mister Micawber]

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'Out' is not a dangling preposition-- it is an adverb in its right place. No comma is required in your response.
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Native English teacher at Mister Micawber's

[BeMyIcon]

Hey, all.
It's my first post here, and I don't want to sound like a total know-it-all,
but I guess with these sort of topics, it's a little hard NOT to, isn't it?
:)

Actually, "out" is not "in the right place", nor is it in the "wrong" place.

It's simply a word within the idiomatic phrase that IS
"hang out".

So at that point, it's no longer "dangling", since it's part of the phrase.

One can make a case for phrases, but that's a different discussion.

To answer the original question: "Grammatically", that's not even a sentence that you're responding with, so the rules are thrown out, anyway; there's no subject; nor is there a verb.

Having said that, it depends on how you want to say it
and what your tone wants to be.

Do you WANT a pause there?

...sorry about all the quotation marks.........

[Mister Micawber]

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Where is it that you think a subject is missing but required, BeMyIcon?
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Native English teacher at Mister Micawber's

[BeMyIcon]

[Mister Micawber]

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It is better not to drink and analyze grammar. It is also more polite to explore a site silently for some time before you decide to contribute.

'Mostly at the Mission' has an understood subject ('I') and an understood verb ('hang out') and is perfectly formed as a natural utterance.
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Native English teacher at Mister Micawber's

[BeMyIcon]

[El Nib]

Thanks for the good advice!