Try putting it in terms he'll understand: "Honey, when you tuck your t-shirts in, it makes me so not want to have sex with you."..

Or better yet...just after he puts his tshirt on before having a chance to tuck it in - rush over and drop to your knees in front of him...and well, you know the rest. Nothing like a little positive reinforcement to get the message across...

Just let him knwo you think he looks so much hotter with his shirt un-tucked and ask why he doesn't do it more often. Then ask him to do it for the day and tell him over and over how good he looks...Hopefully he will get the hint and stay with the trend!..

You know, some guys are just tuck-in-their-shirt kind of guys. Tell him you think it looks more sexy pulled out -- and then do it...