I hate it when people comment about stuff like that. Why do they feel compelled to do it? It doesn't make sense! If somebody is blushing, it's obvious they're embarassed or uncomfortable - so why make them feel worse by picking up on it?
Something similiar happened to me a while ago. I was a this clothes shop, and i had to ask this shop assistant for something. The only assistant around was this really, really cute guy - i would have otherwise avoided, but since he was the only one around, i had no choice. So, the whole time when i was talking to him, i was thinking "Oh my god my voice has gone stupid and squeaky oh my god i'm stuttering oh my god i'm going red" - Then these two girls about my age walk past, and one said to the other - "Look at that girl! She's gone bright red!", and they had a good snigger about it. I could have died. But why did they have to say that? They didn't even know me, yet they were ripping on me. What is the mentallity behind that? I would never laugh at someone i'd never met before - it's just so bleeding rude!
But, as for culprits of this kind of thing - my mum is the worst. Whenever i go out somewhere with her, she's constantly picking people out "Oh, look at that fat woman over there! She shouldn't be eating that doughnut..." or "Look at that girl. Those heels are way to high for her. She can't walk properly in them," - things like that. She thinks she's whispering when she says stuff like that, but she has a VERY LOUD WHISPER. Everyone can hear, and it's terribly embarassing. But i don't understand why people say things like that. If somebody is dressed funny or got a stupid hair style or something, laugh about it IN YOUR HEAD instead of telling the world, and making that poor little person feel daft and self-concious.