I walk stiff!!help!?

my boyfriend is always telling me that i walk stiff i try not to walk like that but when im walkin stiff i dont even notice it..i feel bad that hes always tellin me that n he gets mad everytime i walk like that with him...sometimes im afraid to walk another way because people already think im conceided (im not conceited i dont know why they think that) and if i change my walk they might think more im conceided =[ what should i do i feel really bad right now