(adj) a term to describe the feeling of fun and excitement while appearing to be bored and unthrilled. This word can also be used as a noun.
Ex.1: Let's hang out at my place and play some cards; it'll be a shimmay night.
Ex.2: I saw Jerry get his shimmay on at the bar last night.
Jenny is quite the shimmay; her idea of a good time includes playing golf, watching movies, and chatting with her friends.
The opposite of someone who would be considered a "shimmay" or a "shimmarian" is someone who typically likes to "party" in the old fashioned sense of the word (dancing, drinking, etc.)
Another example of someone acting shimmay would be some guy totally shredding a guitar while keeping a very straight face.