of all things
Of all the possibilities (this is the most surprising or unlikely). When he retired, he took up painting, of all things. He had never even picked up a paintbrush before that! After spending his childhood in and out of detention centers, he became, of all things, a cop.
Of all things!
Can you imagine?; Imagine that! (Usually said about something very strange.) She wore jeans to the dance. Of all things! Billy, stop eating the houseplant! Of all things!