I have seen it in quite a few chats on Facebook and Twitter.
The word sic is probably used as an adverb here -
You may observe this on chat and social media in the context wherein the opposite person writes it intentionally though knowing that the word is misspelled.
When it is used in brackets it means so or thus to show that an odd or something doubtful reading is what was actually written or printed.
Example from OALD:
Here, the word it's is incorrect but copied from the original document. You know that this is incorrect but still will have to write. To show that you are aware of this mistake, you put (sic) after a wrongly spelled word.