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.

Friend: "So yeah, I know I've been telling like every gory detail but ..."
doorbell rings
You: "OMG, my pizza is here! I've got to go, sorry!"
Friend: "No problem..."
You: "ttfn kthx bai"
Friend: "Bai"

ttfn kthx bai by Mad Money Willy G August 29, 2018