Pec shots aren't hard at all. If you've just worked out pecs and there is DOMS, then sometimes they can get a little twitchy when you reach around which is sort of nerve wracking. That aside, there's little to no pain. That includes both injection and the residual pain afterward.
Once you pin them you'll wonder why you never did it before. Start with a smaller volume of something water based like a peptide, injectable vitamin or something... I did it with vitamin b12 in case I would puss out, but I never did. I just get a little twitchy if I worked out chest the day before. Pec injects are great.