ttfn kthx bai

While this literally expands to "tah tah for now, okay, thanks, goodbye..." the pop culture connotation is that you are making a flippant or perhaps merely hasty retreat from a conversation with the speed of a 1980s or 1990s Anime school girl. The character of Yukio in Deadpool 2 comes to mind, as well.

One can also shorten it further as "ttfn kthx bai" or "ttfnkthxbai".

Certainly related to, though a nuance in use of the constituant parts "ttfn" "kthx" and "bai". The "ttfn" adds a friendly aspect, while the "kthx" adds snark, followed by the finality of "bai" - when combined it forms a powerful and ambiguous immediate ending to a conversation, though ironically is often not the last words. It's quite common to have the other party respond with expressions of either offense or solidarity with your assertion using this phrasing.