what's the problem ?

I'm 17 and I live with my grandmother I've noticed if I come out my room with no bra on she'll say "go put a bra on there are men here ( my dad , her husband ) " or "those are too big put a bra on" i understand if I had a tank top or a low cut shirt on but I wear big shirts and long sleeves so I don't see what the problem is ?? although it is her house so i respect her wishes