Wallflower noun
A person who comes to a social event, such as a dance or party, but doesn't get involved in activities because they are shy or unpopular.
He looked confident but turned out to be a wallflower.
John used to be a wallflower. Now, however, he is a very funny, engaging guy whenever he joins parties.
Don't be a wallflower, Mary. Pair up and dance.
The idiom "wallflower" is derived from the plant, the wallflower, which grows by clinging to walls or rocks. The idea is that the person in question is clinging to the wall rather than taking part in the activity.
To say, or believe something or someone that seems completely crazy, delusional, or stupid
You spent 1000$ on a new pair of shoes! It is insanely crazy. You need your head examined.