Ignorance: n. Lack of knowledge, education, or awareness. In other words, just not knowing. How many people know that wearing flip-flops (and 99% of footwear in general) at any time, not just in the gym, is detrimental to posture, gait, and overall musculoskeletal health? Maybe a handful within the fitness community, to say nothing of the general public. It's just walking, right? And footwear is normal, right? Better flip-flops than getting ringworm, right? This person may not have known any better, but not-so-common common sense would say they did, hence "stoopid"--after all, there aren't a million other places to just go take a walk, shod or not, that don't require driving to get there or electricity to operate
You brought up the point about how the responses in this thread (all three of them at the time) are "sad" since someone to wander in and get self-conscious. In reality, it's the people on this and other similar forums who would be the ones to face self-consciousness since, by and large, we train intelligently and therefore abnormally. It's the yahoos on treadmills in flip-flops that are more "normal" than we are
Here's to being abnormal!