You have the usual things like heights, spiders, the idea of a Premier League without Aston Villa.
They don't bear thinking about.
But few could compare - nothing could compare - to the pressure of impersonating Roy Keane. In front of Roy Keane.
The Republic of Ireland squad visited the Olympia last night ahead of their clash with Poland on Sunday and they took in one of the country's hottest musicals.
It just so happens that it's based around the life of their assistant manager.
Imagine coming out to do your normal show, about to open with your first line in your most convincing Cork accent when you feel The Stare coming from the crowd.
Imagine you were one of the players sitting beside or around Keane. Do you laugh? Do you tut? Do you get the hell out of there?
The man himself was snapped last night with writer Michael Nugent. He gave nothing away anyway.
Tough crowd.
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