Many years ago, when I was a teenager, my best friend and I decided to commit our friendship to a new level. We decided to become blood brothers. Now, I don’t even know if people still do this or even if it happened in the past and is just an urban legend. A quick glance at Wikipedia says:
Blood brother can refer to one of two things: two males related by birth, or two or more men not related by birth who have sworn loyalty to each other. This is usually done in a ceremony, known as a blood oath, where the blood of each man is mingled together. The process usually provides a participant with a heightened symbolic sense of attachment with another participant.
Somehow we had some instructions about cutting our forearms and then clasping arms together so the blood mingles. We misread the instructions! Rather than a cut 5cm from the wrist we made a 5cm cut from the wrist. Our blood was mingled. That was in around 1988 and we remain the best of friends today. In fact he was my Best Man at my wedding and we still share the same music tastes and go to concerts together.