you do what you would normally do and ignore them. they are there for the purpose of prevention of shopilifting. try to rationalize it be thinking that something you did or your behaviour somehow matched that of a previous shoplifter. you are there on your own business and if you did nothing wrong then you shouldn't have anything to worry about. just do what you do. and if it really annoys you that much, then just leave to make things even more suspicious.
maybe the guard was interested in you and found you attractive.
and if the guard lays a finger on you or stops you by use of physical contact, then you scream 'stop groping me!'
there are many ways to turn the situation around.
i hope this incoherent response has found a way to make sense to you.