Some children do go through this phase. Not much advice here just re-assurance but my daughter did it too- to the extent of stripping off whilst we were in the audience of a talent show. I did insist on the potty training pants but she decided herself to get potty trained so she could discard of those. The phase lasted about a year. She stopped when she went to pre-school, although refused coats until she was at school. If you have a strong willed child I found you have to pick your battles ... if this is important to you, just keep insisting but the phase will pass.