When you send or respond to a text without fully thinking about the consequences of doing so. Similar to drunk texting but you're completely sober. Its more just plain impulsive
Example 1:
Father: You stayed out too late at that party last night; you're grounded for the next week
Son: Fuck you old man!
Father: make that the next month
Son: C'mon dad, that was my text reflex!
Example 2:
Texter Dude 1: Hey baby, you wanna go hookup behind the bleachers?
Texter Chick 1: Hell no you creeper! WTF is up with u? Drunk?
Texter Chick 1's friend: Yah, that was his text reflex