If you consider that people always do their best work when they are treated fairly and with enthusiasm, why would anyone in a leadership position (boss or peer) treat someone any differently? How many times have we seen someone (or been someone) getting chewed out, diminished or made fun of? Treating people with a lack of dignity and respect is probably the single greatest threat to being successful...at anything.
If you can only spare enough time to make one adjustment...this is the one.