We were practicing jo suburi and a guy near me wearing a brown belt was doing very bad, pushing the jo without sliding but just gripping it very tight and moving it like pile driver. I told him in a polite tone that he is doing it in a wrong way. He looked at my belt and says " who the fuck do you think you are, a sensei??"
1.) Maybe he was having an off day
2.) Maybe what he was doing was new to him (not everyone does weapon work the same way- even in the same affiliation)
3.) I wouldn't have said anything. I just would have let him do his thing and I would have done my thing. At the last seminar I attented, I wasn't sure of who was senior to me and there were times my partner was doing something wrong or insisting I do it wrong and I either said "Lets watch another group for a sec." or just kept doing it wrong until the sensei came around and corrected us. I didn't feel like it was my place to correct them because I had no idea where they stood in their training. Sure, I looked like I didn't know what I was doing, but I would rather that then put my foot in my mouth.
4.) If this happened a few years ago, why are you bring this up now?