The abbreviation given to the most common and uncreative excuse for ones actions while on the net.
The excuse will most commonly blame the younger brother and is used for just about any embarrassing or demeaning mistake, whether the regretful accuser has siblings or not.
Admin: Fail hacker is fail. Enjoy your ban.
Hacker: Oh sorry man I let my lil bro on my computer. He must somehow know the exact server I play and decided to hack on it.
Admin's response: Oh the old MBDI excuse? Next you'll be saying your cat got you banned!
girl: This e-relationship is over! I thought we were friends but it turns out your just a sleaze. Why did you try to cyber with me and send me pics of your cock last night you sad little boy.
boy: Who me? oh no.. that was my little brother on msn, I told him not to speak to any of my contacts!
girl's response: Don't pull that MBDI s*** on me!