Originally from 尊い (toutoi), meaning precious, valuable or priceless, it became Japanese internet slang "ていてい (or てぇてぇ)" roughly meaning someone else's actions are wholesome, or precious.
Popularised in the west by subtitled V-Tuber clips, where it was used typically during moments where the V-Tubers were acting affectionate to one another; this hard to translate word was often simply romanised. This resulted in several spellings, the most popular of which seems to be "TeeTee", whith other variant such as: tee-tee, tee tee, tei-tei, TT and te-te.
The ability to nimbly use the keys for texting; phone prowess for the digital age.
After fumbling with the cell phone for several minutes, my daughtertook it away from me, quickly sent the message and told me, "Dad, you have no texterity!"
I texted my friend to come over for a brunch but text went come over for a punch. After several back and forth texts to clarify I could see this was another textmess.