Such silly or goofy behavior is almost always of a good nature, and involves good, sometimes clean fun.
Said behavior will usually happen when all or most people in said group are either bored, hyper, or overly tired.
It can also be identified as the actions done by said group that come about as a result of the friends in such group "getting high off of each other", a phrase used to describe the feeling of being high when around certain friends for a given amount of time, simply because they are awesome and fun to be around and they always have fun together and their company is very much enjoyed.
Shenanigans is also, but less often, referred to as sneaky, deceptive, or mischievious behavior.
*Peter sitting by himself*
*Several friends approach him*
Kim: Hey, man, there's room over there with the rest of us if you wanna join.
Peter: Yes, I'm aware.
Kim: So you wanna sit by yourself like a loner?
Peter: Yeah, I'm fine, thanks.
*Kim and others return*
Leila: What's wrong with Peter?
Kim: Nothing, he just wants to sit by himself, and not join our super-fun shenanigans that we are having.
*All other than Peter (sad face) commence in having a super-fun time of shenanigans*
3) Playing improve games with Nick (happy face). Such games include "freeze", "bang", "atom", "the party game", "psychic battle", etc.
4) Having a dance party outside of the chorus room.
5) Having (and losing) a crab fight with Leila, resulting in accidentally banging your head against a chair.
1) A wild goose chase; Many clues that potentially lead to one impressive prize or outcome, but not always.
2) Pete Wentz and Fall Out Boy related-stuff on the internets
Person 2: "Oh, you know Pete Wentz and his shenanigans"
Favorite place to eat for Officer Farva.
Farva - "You mean shenanigans, you're talking about shenanigans, right?
Effects of shenanigans can result in mental and emotional trauma and instability, commitment issues and loss of libido.
"Yeah she fucking left me at K-Mart alone, 50 miles from home."
Guy: I DECLARE SHENANIGANS!!!!!!!
Guy 2: Everybody find a broom!!!!!!
Everybody participates in broom fight