My girlfriend from Texas now living with me in Canada has had me translate very quickly in my mind between C and F. Same thing for kilometers and miles.
I was camping in the mountains last weekend and gassing up at a tourist spot. Someone asked "how many litres in a gallon". I yelled out "3.8". Then they asked as a joke "how many kilometers in a mile?" ... "0.6". As they drove by me leaving the parking lot they were smiling, and they asked "it's 14C right now, what's that in F?" ...it takes me a few seconds to calculate, and I said "about 56".
It was a cute moment for myself and the people who were visiting from California.