The act of taking a prearranged hang-out time with one or more friends, and folding / inviting more, previously unmentioned and usually unnaproved friends to come along. Typically this is done because the "friend consolidator" has found somebody they find more interesting to go to the same event with but don't want to break plans and be an @ss, or because they are flakey and forgot the original plans in the first place.
Person1: "Hi, this is my new and far more interesting friend, hope you don't mind if he/she tags along to your Birthday Party!"
Person2: "Of course i mind! What a shameless act of Friend Consolidation! :("