A Double daboosy dare is similar to the triple-dog-dare
, you should not / cannot back down from it, however unlike the triple-dog-dare you can be given an alternative which MUST be worse than the origional dare.
Mark: I double daboosy dare you to go to town dressed in drag
Dave: No way!
Mark: Well, your only alternative is to go to the party tonight dressed in drag and tell that girl you like that you are coming out of the closet