I'm not a huge fan of screaming, ranting preaching... the kind that leads to a minister throwing off his coat, pulling off his tie and pulling his shirt tails out of his pants,... But if someone is dressed more casually from the start with an un-tucked shirt... well... that's OK with me. Young people tend to be much more casual in their dress without seeing it as disrespectful.
Although I have to say that one of the biggest laughs I ever got in church was from an 'on fire' preacher who was ripping off clothing and un-tucked his shirt tails... He was not a very tall fellow but ws kind of big around and the tails were below his knees! He definitely had the Jesus look going after that!