Perhaps central/south Texas is different, because we're used to people wearing as little as possible during the summer anyway (including bathing suits, if water is within a 10 mile radius). But I've never really noticed anyone caring what someone wears into a casual restaurant/convenience store/whatever. at least in the middle of the day.
I often stop at a nice little place (Stella Public House near downtown San Antonio) on Saturday or Sunday afternoon in whatever I wear to ride (they have a great beer selection). I had on spandex shorts and a muscle shirt the last time, and no one gave me a second glance or acted weird.