Scissors, Newspaper, Stoned
I've done it with a handheld shearing device; that wasn't too bad because I could manage to keep it a similar length, but the worst was when I went through a phase of random spikey hair. This involved mirrors, awkward angles I couldn't work out, reflections within reflections. My eyesight's not as good as it used to be and I'd always do it when drunk or stoned. Clumps of wet hair dropping on newspaper.
At work I told them I'd found an existential barber - Monsieur Jacques Sartre - who was quite happy to give me an Egon Scheile/Wittgenstein hair-do. They didn't believe me, of course.
I've given it up for now, having found the courage to go to proper places.