Mini-Dachshund/Yorkshire Terrior Aggression

I have a one and a half year old Dorkie, who recently has snipped at one of my roommates. He has done this twice in the past three days. He knows her very well, we have lived together for a year now and has not done this before to anyone or any other animal. The dog was on the bed the first time and she just picked him up and started playing with him when he snapped her, the second time, she picked him off the bed and put him onto her lap in a chair and started petting him and then he snapped her. I don't really know what to do or what is really causing this but I'm afraid he is going to do it again and maybe to someone else. He has never had any aggression problems before, people have taken toys/food and moved him before and he was completely fine with it. Does anyone know what could be going on or could help me?

First you have to determine if it is a medical problem or a behavioural problem. A vet check is in order to rule out or confirm the fact your dog may be experiencing pain when handled or anything similar. Sudden change in behaviour is quite often health related. If it is not a health issue then I would suggest that your Doxie is showing dominant behaviour towards your roomy. NILF is a great protocol for establishing leadership. The dog may also be laying claim to the bed, in which case removing bed privileges may be in order.

Good luck and keep us posted!   

Always rule out medical problems first.  If that reveals nothing out of the ordinary, then it's time to consider that your dog is starting to make some decisions about what the rules are.

One of the things that toy dogs try to control is the timing of being handled.  First, make sure everyone who will handle your dog, knows the way he likes to be picked up and held.  Every dog is a little different in what they are comfortable with.  Think of how he reacts to various ways you pick him up and hold him - there will be a way that he seems to associate most with safety and security.  

Next, make sure you are setting the rules.  NILIF for little dogs means that you decide when your dog is picked up, and when he leaves your lap.  Do not ever let him either jump up or climb down, but rather pick him up and put him down.  For safety reasons, it's better that way anyway.

You may have a surprise the first time he tries to jump off your lap, and you say "No."  Hold him gently until he relaxes and will stay put without your holding him, then tell him he's a good boy and immediately put him down.  If he chooses to start a battle with you, gently and calmly take him to his crate and put him in a time out.  About three minutes is long enough.  Repeat the next time you hold him in your lap.

Until you've worked all this out, I wouldn't let your roommates handle him.  It won't take more than a couple days to get your own pattern settled.  Then inform your roomates of the new rules.

On top of this, consider taking a tricks training course with him.  When you take away freedom, you have to offer a place in your life in return.  When this sort of behavior emerges at this age, it's often traceable to the boredom of a clever dog who's really seeking nothing more than a bit more of an active role in your life.  If you won't give him some work to do, he'll make some up, including this game of "I'm thinking of a rule, and if you guess the rule wrong, I'll bite you."