Weaseler is a term given to someone who invites or invited themselves to a private event. This person or peoples do not understand that the organisers do not want them there. The weaseler, otherwise know as a weasel, may invite other parties to the event performing the ultimate 'weasel'.
Such circumstances can be avoided by not making the event public (e.g. on facebook or twitter) and avoiding talking about the event around a potential weaseler.
Weaselers can be identified by the lack of social life, obsession with one or more of the parties and an overall interest of the event.
A weaseler can be identified by their hand gesture. The back of the hand is placed under the chin with the fingers facing outwards. The weaseler then moves the fingers in a waving motion such as tentacles flailing from the body of an octopus.
Boy 1: Hey man want to come to the shopping mall?
Boy 2: Yeah man, fo sho, what time?
Boy 1: How about 2?
Creep/Weasler: Hey guys, what time is it again? and where are we meeting?
Boy 1: No creep. You can't come. You are such a weaseler.
Girl 1: I had a party last weekend and that creep just showed up.
Girl 2: Really? What a weaseler.
Girl 1: I know. He is such a grish.
Girl 2: One time I was on a double date and he invited himself and a girl. He performed the ultimate weasel.