You have attempted to cut the tip of your finger off with a very sharp blade. Do not cry.
In this first step you'll want to wrap your finger and hold it above you're head like you've been taught to do.
It should only be a few seconds before curiosity sets in and you peel the wrap off to have a look. At this point you will want to photograph your injury, otherwise you'll be met with 'no pics-didn't happen' from your friends.
Step 1: Explain your current position to those around you.
Start by yelling "I'VE DONE SOMETHING BAD."
The response will probably be, "Haha. Is there blood?"
The appropriate reaction is, "Uh...yeah. Yeah, some blood."
At this point all people within earshot will probably stop laughing and run to your side.
None of them have cars because you live in 'bike friendly' Portland, Oregon. Your friends will direct you to the closest bus that will take you to the closest hospital.
Get on that bus. Explain to the bus driver what you have done and calmly take a seat near the front.
Take your paper towel wrap off again and watch the faces of the strangers around you. They may be upset that you are assessing your injury in such a public place. Take another picture.