When my youngest son was about a year old we discovered that he was lactose intolerant. At about 3 years of age, when he started going to birthday parties, pre-school, etc., we started to educate him about staying away from foods containing milk and milk products so that he could avoid the gastrointestinal effects they caused.
Fast forward to the age of 4 1/2 or so - we are out for dinner at a nice restaurant. The kids are dressed up and on their best behaviour. After dinner the waitress, who has taken a liking to the good looking boys who are so polite, says because they have been so good she is going to bring them both a big dish of ice cream.
Son says calmly and with perfect diction, "I can't have ice cream. It gives me the shits!" Every one who heard just howled with laughter