I don't know who sb is, but he or she is incorrect. When entering a / command in game, it will attempt to interpret abbreviated commands for full commands, thus typing /dis will be interpreted as /disband.
When posting a message to this or any forum, it would be very helpful to provide a little bit more detail, explanation, and be aware of your grammar. People are less inclined to take a post seriously if it appears the poster did not take the time to make his or her post more readable.
If you wish to Disable Combat Experience, right click over your XP bar and select the option "Disable Combat Experience." If you have any further questions, please reply.