SDD stands for Slightly Drunk Driver.

Very similar to a designated driver. The SDD will still drink but they will not get as wasted as their friends.

Because being sober around people that drunk is no fun.

Soft Dick Dennis When under the influence and attempting to preform sexual intercourse the penis may become inerectile.

Serious Deep Dicking.

SDD means small dick disorder.

Acryonym for "Software Design and Development", a HSC subject. Basically, it sucks, and should be avoided at all costs. Even the teachers who teach it will tell you not to enrol in it because it sucks. For the tiny bit of programming you actually get to do, you'll have to use some terrible MS language like VB or C#, but most of the subject is incomprehensible project management mumbo jumbo.

(n.)--Sarcasm Detection Disorder. The inability to properly assign sarcastic intent to electronically transferred words. Often occurring on AIM, Facebook, and other online chat forums. Usually results in confusion and hurt feelings.