Milk. Most dairy I am fine with, but drinking a glass of cold milk gives me the worst griping pains in my stomach, then if I have a coffee that is all milk (Latte) I will feel really mega bloated.
This. My mom and I are both moderately lactose-intolerant. Eating cheese and stuff doesn't bother me, but if I down a milkshake or a latte or an excessive amount of ice cream it does not feel great at allll.