The first clue that the person you are dealing with is a total whack job. Just as an iceberg is largely hidden below the water’s surface, the tip of the nutberg is a hint of the vast crazy hidden deep inside your typical head case.
Xavier: Did you see that old lady flip out when she thought we were laughing at her cat?
Emmett: Yeah, that was weird. I think we just saw the tip of the nutberg.
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since O’Connel’s time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before O’Connel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. Penguin Books,1992. p. 38)