It’s your middle finger ㅗ

when you're hungover as shit after a spending a night drunk as a skunk

It is one of the Korean vowels, which has an 'o' sound when pronounced.
If you send 'ㅗ' over text to somebody, you are showing the middle finger to him/her.

A Korean vowel pronounced like 'oh'. It requires at least one; at most three Korean consonant(s) to complete a letter. However, it is solely used to flip people off when texting.

A Korean vowel that is usually used by itself if it is to flip someone off when texting due to its resemblance to a "middle finger".