The act of having multiple conversations at the same time on an instant messaging service, not necessarily AIM, e.g. MSN-juggling, ICQ-juggling, etc. It can also lead to a person's social downfall.
I was talking to Alexis the other day, and I could totally tell she was AIM-juggling me. What really gave it away was when she called me "Lance" and sent me a pic of her totally nekked.