When you try not to be rude texting while you are out with friends so you hide it by texting with the phone still in your bag. This is an attempt to trick people that you are with into not thinking you are rude when in fact it is so obvious when you are standing there with your bag open and your whole hand is in the bag, holding your phone, texting.
"Hey! what are you looking for in your bag, Jenn?" "Oh nothing, I'm just bag texting".