Apparently there is a triangle of death on the upper lip. does this make it dangerous at all to remove (tweezing, threading, waxing etc) upper lip hair?

The lay term "triangle of death" refers to an area of the face that has venous blood flow that leads into the brain. Infection that enters that venous blood can travel the route and infect the brain substance triggering a fatal infection. Such chance infections are rare with simple cosmetic manipulation of the facial skin. It would be a concern when manipulating local infected tissue.