If you're scared of your father you should take your underwear off whenever possible and hide it. Obviously, if you have to dress or undress in your father's presence you'll have to be careful, but as soon as possible take it off and hide it somewhere where you can retrieve it when necessary. Yes, put it in the laundry unused - nobody will say anything so long as it's there - just goes to show that underwear is just a matter of convention and serves no useful purpose. Be yourself, be free !