Living in a fool's paradise
Suggests a state of illusory happiness or security (Romeo and Juliet).
Rapturous
Filled with intense delight or enthusiasm.
...a rapturous standing ovation...
Irate
Feeling or showing anger.
The customer was quite irate when his order was delayed.
Congenial
Pleasing or liked on account of having similar qualities/interests
As fellow cat lovers, Corelyn and Emilia enjoyed a congenial friendship.
To go down the rabbit hole
To enter a bizarre or confusing situation or line of inquiry (from Alice's Adventures in Wonderland).
The milk of human kindness
Refers to compassion and empathy (Macbeth).
Gratifying
All students in the class had failed their common test. Their English teacher found it gratifying.
Belligerent
Hostile and aggressive.
The man's belligerent tone immediately put everyone on edge.
Equanimous
calm and composed
Despite the overwhelming nervousness, John remained equanimous throughout his performance.
A Promethean spirit
Describes someone who is boldly creative, rebellious against authority, and willing to suffer for their knowledge or ideals (after the Greek Titan Prometheus).
Brevity is the soul of wit
Describes someone who is concise and clever in their speech (Hamlet).
Vindicated
the feeling of relief and satisfaction experienced when one is proven correct or cleared of blame, after being unjustly accused or doubted.
Alienated
Feeling isolated and estranged
Being the only person who does not speak Chinese, Nick felt alienated from his peers.
Blithe
Showing casual and cheerful indifference considered to be callous or improper.
With blithe disregard for consequences, the boy skipped down the steep mountain path.
Cross the Rubicon
Making an irreversible decision/passing the point of no return.
A man for all seasons
Describes someone who is adaptable and respected in various circumstances (often used in reference to Sir Thomas More, though the play is not strictly Shakespeare's, the sentiment aligns).
Rapt
Completely fascinated or absorbed by what one is seeing.
The children listened with rapt attention as Mr. Neil described his recipe for....
Wistful
Having or showing a feeling of vague or regretful longing.
Crimson wistfully glanced at the photograph of her old friends.
A shadow of his former self
Describes someone who has lost their vitality, strength, or former qualities (common literary trope).
To meet one's Waterloo
To encounter a final and decisive defeat.
A green-eyed monster
Refers to jealousy (Othello).
Sanguine
optimistic or positive, especially in an apparently bad or difficult situation.
Contemptuous
Expressing scorn or disdain.
The teacher's contemptuous gaze did little to put up a farce of impartiality.
Placid
Calm and peaceful with little activity.
Not easily excited.
The ordinarily playful boy was uncharacteristically placid on the day of the competition.
A good Samaritan
A charitable or helpful person, especially to a stranger in distress (from the biblical parable).