When you develop a small to large callus on the tips of your thumbs from excessive texting. Or when you develop "pads" or flattened harder areas on the tips of your thumbs.
"Dude, I think i've got texter's thumb, just look at this callus."
or
"Wow, that is some impressive texter's thumb."
"I know, I think i text too much."
The feeling that ultimately overcomes oneself upon sending a text message and either; writing the wrong thing, sending it to the wrong person, or forgetting something, knowing that you cannot now take it back. Usually ends in grief that you now have to send more messages to take back your original or add to it.
Occurrences range from the subtle to the major that may alter the conversation.