You should pack a 'change of underwear'. [=additional underwear that you can wear at another time]
He answered the door 'in his underwear'. [=while wearing only underwear]
(..) Well, let's try one more. There you go. Ernie's, ? I'll be there. And if things go well, maybe this time... ...I'll get to see your underwear. No one was around to hear that? So what'd he say? What a jerk! I kept talking about you, and he kept asking me out. (..)1996 TvShow: Friends Title: The One After the Superbowl: Part 1 Season: 2 Episode 12
(..) Why are you looking at me? He's the one who wants to boff the maniac! Are you okay? No. I'm just nervous. Maybe if I just picture them all in their underwear... That's not a good idea. That's the reason the last guy got fired. I'm used to playing for grownups. Grownups drink their coffee (..)1996 TvShow: Friends Title: The One After the Superbowl: Part 1 Season: 2 Episode 12