Are There any parts of the body NOT suitable to be spanked

My examinees enjoy having their testicles tapped firmly.

For me nothing excites me more than spankings that are administered to a bare bottom, both female and male. Only exceptions is my wife occasionally likes to be very lightly hand spanked on vulva. I believe it’s the vibration of the light spanks and not the impact that she likes.

Here is a diagram (scroll down a little bit) https://www.thedeviatenetwork.com/single-post/2016/05/10/BDSM-Basics-Impact-Play-Safe-Zones-and-Spanking-Tips to show areas one should avoid when spanking or doing impact play.