Initialism of what the fuck.
"He typed wtf in lowercase to match the casual tone of the chat message."
Alternative letter-case form of WTF
World Taekwondo Federation
"The athlete proudly waved the flag representing his country while competing under the World Taekwondo Federation banner."
The acronym WTF originated as programming slang from The Daily WTF, a popular humor blog that shares stories about poor coding practices and software disasters. It was adopted to express shock or disbelief at the absurd situations described in these articles before spreading more broadly into general internet usage.