Do you hate when people try to guess your mood?

People expect me to walk around with a manic grin on my face 24-7! Apparently i have a 'sad face' when i'm expressionless.... That's always got on my nerves as i don't usually convey how i am feeling through my body language that much. Only people who know me can tell. So it gets on my nerves when you've got someone shrieking that you should cheer up!