Just because you can never have enough acronyms.
Instant Messenger Multiple Personality Disorder (IMMPD):
When you have an identity in multiple Instant Messangers (AIM, ICQ, Jabber, MSN, etc) and log in to all of them at the same time.
Worse cases involve having multiple identities with the same Instant Messangers and logging in to all of them at the same time, eithor via different computers or different programs on the same computer.
NB. This is a joke.