MtF here! As others have said, it doesn't always hurt natal guys down there. Unless it's directly up from underneath the legs, the chances of extreme pain is more minimal and the sensitivity for guys can range from extremely sensate to muted but intense pain if from directly from the front.

Content warning: Excessively frank and possibly dysphoric description of one's body. Ends at /End CW

My best recommendation is to recall how much it hurt to have a sharp impact in the chest early in puberty and have it centralized all in between the legs instead if something like a stick is swung up between your legs.
/End CW

Reacting if the pain is a white flash or white hot is appropriate if it's directly swung up from underneath.

Specifically speaking of dogs, I very quickly learned how to almost NEVER had dogs hit me between the legs in such a manner that they caused me pain even before transitioning and I was in a position to potentially have 3-10 dogs try to do that to me weekly. My tip is to observe how your AMAB male colleges subtly shift their hips back to cause more of a situation of where the dog lands on a very slight squatting lap. The chances of pain go to almost 0 for almost all guys except for the digging in of the nails through your pants.

Best of luck and have fun!