With all the focus on activities that shouldn't be performed while texting, it seems the most obvious of all has been overlooked. That being: texting while texting.
In a recent study of mine (informal, and with no substantiating facts at all) I determined that in addition to the mental confusion caused by simultaneous texting, far more harm can be done.
Jobs can be lost, relationships ruined, and of at least equal importance, you can look like a real asshat. The case for "serial" as opposed to "parallel" texting is made best by examples:
Let's assume you're texting with your wife, as well as with your boss, and you "cross reply":
Wife: "So how did things go w/ur fertility clinic appt?"
You: "I think I pulled it off!"
Or, perhaps, a thread with your Brother, and a simultaneous thread with a co-worker about your lunch order:
Brother: "Uncle Jimmy passed away this morning. Anything special I should tell the Crematorium?"
You: "Tell them well-done this time!"
Obviously, I could go on and on, but I think it's pretty clear that texting while texting can, at the very least raise eyebrows, and at worst, change your relationship with the people you know and love forever.