When I was in middle school, some girls in my class punched themselves in the belly because they heard that was the most sensitive place to get hit. The skinny girls felt the pain, but one really fat girl punched herself in the belly multiple times and said “hey! this doesn’t hurt at all!” The skinny girls looked at each other and laughed while the fat girl was smiling unaware.
Raichu is very fat, so it probably won’t feel much, just laugh from the sensation.