I use "howdy," but only very informally. I would not walk into a meeting with senior management and say "Howdy!" (I use it quite often when I enter a chat room.)
The second question means the people you are talking to will accept you for about 15 minutes if you can be "charming" - talk well, compliment others, be witty, etc. But you have to be able to move beyond having a nice way of spe