Do you hold a tattoo gun at a 45 degree angle?

135 degrees. Supplementary angles add up to 180 degrees so the supplementary to 45 is 180 - 45 =135.

Angles are supplementary if they add up to 180. So, with some algebra 45+x=180 x=180-45=135

it will become 45 degree

if you double a 45 degree angle you have a perfectly perpendicular angle, a 90 degree square corner.