None of the above, so I didna vote. For formal occasions, I always tuck it in. For all other times, there's no conscious "rule" that I follow. I don't mind how a well-fitting shirt looks, tucked in on me. When I go skating for fitness, I usually make sure that the shirt is un-tucked, for ventilation. If I'm only skating for short-distance transportation, especially if the air temperature isn't high, I don't mind keeping it tucked.
My opinion is the opposite of Activebutodd's: tucked-in shirts look more flattering on me, as long as they fit me well. If it's soh wide that it billows out from the waistline, it feels messy to me - all the more reason to make sure my clothes fit me well.
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Why be a label, be yourself and keep others guessing instead. - Dee_.