Why Brits Say "Brilliant": Enthusiasm, Exaggeration, and Irony

British usage of "brilliant" is versatile:

• Genuine enthusiasm/approval: "That's brilliant!" = excellent, wonderful.
• Exaggeration for emphasis: "The movie was brilliant!" (even if not perfect).
• Irony/sarcasm: "Oh, brilliant!" after a mishap = "that's terrible."

Context and tone determine meaning. It's a quintessentially British linguistic tool for expressing strong positive—or mock-positive—sentiment.