I always smile when going up our last very steep hill towards home. There are frequent cars and I don't want them thinking "OH I bet she's sorry she's on a bike- she must be miserable!".
I know I feel like joggers are miserable when I see their grimacing faces of pain.
I don't want any one thinking I'm not thoroughly enjoying my biking!
I often catch myself smiling a big smile when I'm riding my bike.