Man of Honour
[..] In terms of pain it's like a flu jab so not very I think. psychologically you have a needle up to your face so things are unnecessarily amplified.
I think that's the key point. There are strong primitive instincts against piercing wounds and all the more so in your mouth. Intellect says "It's OK, just a minor thing being done for a very good reason", instinct says "GET IT AWAY GET IT AWAY".