Given a category and a set of five words, find the word from the set that does not belong (i.e. is the least relevant) with the other words in the category. Words are separated by commas.

Category: emotional display 
Words: buck, identity, culture, fawn, pester
buck

Category: shady activities 
Words: loosen, smuggled, chocolate, wrongful, fudge
chocolate

Category: temperature 
Words: mild, refreshing, freezing, optimist, cool

optimist