"To wear" is the general meaning of all three words, but "don" and "sport" have different connotations than simply wearing. "To don" means "to put on". To deliberately be putting on specific clothes. In my mind it would be an outrageously good-looking outfit or a costume or a nice hat. It is usually used in the third person: "Jasper donned a red sweater". It would be a lot less common to say: "Tonight I am going to don a dress", you'd just say: "I am going to wear/put on a a dress". "To sport", is also used in the third person, "Jasper is sporting a red sweater tonight". It has the connotations of showing off, as it says in dictionary.com: "to wear, display, carry, etc., especially with ostentation; show off" http://www.dictionary.com/browse/sport?s=ts