Things I do to keep my cool when biking in traffic:
1. When a driver honks at me, I smile and wave as if they are someone I know just saying "Hello." I love the puzzled looks I get.
2. When a driver does something well (or something kind) - stays behind me until it is safe to pass, passes me with at least 3 feet between their rearview mirror and my handlebars, slows down to let me in when I signal a lane change, etc. - I let myself really feel the appreciation and wave my "thank you" to them.
3. When a driver does something that threatens my life or safety, I wait for the adrenaline rush to wear off (and sometimes I say a few choice words out loud to help with that) and then breathe a blessing: "May you get where you are going efficiently and safely." (I do this when I drive, too.)
When possible I ask, directly, for what I want. While sitting at intersections waiting for the light to change, I've asked the driver next to me, "OK if I move in front of you until I get around that delivery truck parked in the bike lane?" I've never had a driver say no.
And sometimes I just have to laugh. For example, once I was nearly sideswiped while being passed by a woman driving a Smartcar with a vanity license plate that said "GoGreen." I guess I was a little too green for her. I glided up next to her at the next traffic light and her window was down, so I broke wind really loudly. Very satisfying.
What do you do to keep your cool when working under pressure?