Final answer:
The phrase 'what a real nut' is an example of figurative language where 'nut' figuratively describes someone acting eccentric or crazy.
Step-by-step explanation:
When you and a friend understand the phrase 'what a real nut' to mean that someone is acting crazy, you are applying figurative meaning. Figurative language involves using words or expressions with a meaning that is different from the literal interpretation. In this context, 'nut' does not literally refer to an edible seed, but rather it is a slang term implying that someone is behaving in an unusual or eccentric manner.