In over a decade of teaching participatory partner dance, it's amazing how many times the hard work I put into welcoming new people, is undermined by well-meaning individuals giving feedback - particularly to beginners.
The giver of feedback is thinking, I'm helping this person - they're making a mistake. I need to tell them how to do this step, I've been dancing for years - I know it all.
The receiver? OMG, who does this person think they are? I can't believe they're telling me that I'm doing it wrong. I feel 'this' small right now. I can't wait to get out of here and never come back. They're not even doing it like the teacher.
I can tell you from our comprehensive system of feedback and observation - both formal and informal - that people naturally avoid confrontation, so will smile, nod and then vote with their feet - by avoiding dancing with you, complaining or stepping out of the community altogether.
Given the fact that they majority of people who step into classes are doing it to build confidence, make some new friends and have a laugh - an experience like the one above is a complete fail against all three.