what's wrong with smiling?
Smiling is a great way to enter a set/ room with what style called the 'I just bench pressed the world' smile
My thought would be that if you are entering a set you want to be perceived as coming in non-threatening to win over the obstacles and possible amogs initially so you can demonstrate higher value n deal with the challenges as they arise.
whats 'cool' is another matter and I think being cool is about who cares less... much like negotiating, if you are out with people who admire you for whatever reasons(rich powerful, leader star etc), then you generally don't have to talk or smile much, they tend to do it all for you.
further, A lot of 'truly tough' guys have great senses of humour yet they never smile when there really isn't a reason and don't balk at tense moments... (ever told a joke to a set and have their groups amog just stare at you in the punchline? haha yea...)
I spend a lot of time with truly tough people and the one thing they have in common is that they all remain alpha without having to dominate each other (a fine line between being confident/dominant without being domineering).