"Down to Brady"
(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.
Lady: "My brother and I are going to the liquor store to get stuff for the party tonight."
Friend: "I know you're just trying to get him drunk cause you're DTB".