Most Helpful Guy
Meh, unless it's your house, I guess you don't have the ability to dictate what he wears, which is a shame, unless of course you have that kind of power over him.
I dunno, it's weird but it's not uncommon, a lot of people do it - when I'm alone in the house, I walk from my room to the shower naked, and nip downstairs quick in just boxers, because it's comfy and I'm lazy. I'm guessing your Dad is slightly lazy too. :)
I guess you could try to tell him not to do it, or hint at it by buying him a dressing down or something, I dunno. If you live with your Dad and your Mum, tell your Mum it bothers you so she'll bust his ass and cause him to stop doing it.
It sounds disgusting to me because I was one of those kids who managed to get by never seeing his parents naked or...semi naked. Either that or the horror burned it straight out of my memories and into a boundry box or something.
But no, it's not odd, it's normal. Just, make sure he doesn't do it so you get to see him wearing his underwear, but that would be odd.
Learn some evasive manuoevers and roll from cover to cover in your house - it's your only hope!