my son was very similar at that age i used to get so embarressed cause he would do it at the most random times eg. shopping, dinners etc.. i think you get the picture.. I guess he sort of grew out of it but i used to take the toy off him and not give it back no matter what he did too teach him its wrong.. as for the others they should realise that he is a toddler experimenting with his boundaries and you as a responsible mother have to do what you need to do to teach him things in life, its a playgroup not a school exam and if they know better tell them to show you better.. kids will be kids and some kids arent the angels other people think their kids are.. Cause they all are but its all a learning process and they should support that. just my opinion