What is the smallest manned jet aircraft?
The BD-5J is what guinness world records claims to be the smallest but it is larger than the Cri-Cri in its jet implementation (the BD-5A is smaller than the Cri-Cri but prop powered)  

If you want to count really experimental stuff the Martin Marietta X-24A lifting body has a wingspan of only 11 ft 6in. making it the smallest. Although I will admit it is predicated on a lose definition of "wing" and is rocket (not jet) powered.     

Although if you broaden your definition of "aircraft" Yves Rossy's jet wing backpack is the smallest coming in at a wingspan of 7.9 ft. It is still piloted, jet powered although I do not think it can take off under its own power.