(as in Brady Bunch)
1. When a person is interested in only hanging out with his brothers/sisters (or, bros and hoes) on the weekends rather than engaging in social activities with new people.
2. When a person is so close to his brother/sister that they appear to be dating or interested in hooking up with one another.
Friend: "I know you're just trying to get him drunk cause you're DTB".
Guy1 to Guy 2: dtb?
Guy2: sure, gimme a min.
Guy2 to Guy3: hey man me and a few others are dtb, u in?
Guy3: Fuck yeah, lez bang!