cool as a cucumber

Still he had all his wits about him, and was as cool as a cucumber.

1722, Daniel Defoe, Tweede deel der wonderbare levens gevallen van Robinson Crusoe ... Nu uit het Engelsch vertaaldt, en met een kaart zyner voyagie, en figuren voorzien (translation), page 167

1731, Jonathan Swift, Alexander Pope, Miscellanies: The Last Volume Pert as a Pear-Monger I'd be, If Molly were but kind; Cool as a Cucumber could see The rest of Womankind

Seconds later, Dowd was pointing to the spot again - this time without changing his mind - after Walcott was tugged back by Parker. Fabregas, cool as a cucumber, fired his penalty straight down the middle of the goal.

2011 January 8, Chris Bevan, “Arsenal 1 - 1 Leeds”, in BBC

“I’d be shaking in my shoes to ride in the Preakness,” said Desormeaux, who finished dead last in his first Preakness in 1988. “Now, not only have I won it twice [in 1998 on Real Quiet and in 2008 on Big Brown], I’ve lived life. I’ll be as cool as a cucumber in the saddle” with Exaggerator on Saturday.

2016 May 17, Don Markus, “For Kent Desormeaux, Preakness is a welcome Maryland homecoming”, in The Washington Post