Lactose intolerant is when someone can't eat dairy foods because of the lactose content. When someone who is lactose intolerant eats dairy without taking a pill, that person has horrible bellyaches.
Originally, people in the world were all lactose intolerant. Their bodies ceased the production of the enzyme lactase after an early age.
Their diets did not contain much milk anyways, so it was not a problem.
Somewhere in Europe, a mutation occured where lactase continued to be produced through adulthood.
Lactose tolerance is a dominant allele, so the trait became very common in Western Europe.
The friend that never shutsthe fuck up about being lactose intolerant. This friend more than likely isnt even really lactose intolerant. This type of friend manages to mention that they're lactose intolerant in every conversation.
Friend 1: "Do you guys want snacks for the party?"
Lactose Intolerant Friend: "As long as there is no cheese. Remeber I'm lactose intolerant?"
Friend 2: "Wow, you're definitely the lactose intolerant friend."
"No, I'll takemy coffee black, I really can't have milk at this time of the day. I just got diagnosed with C.L.I, better known as Circadian Lactose Intolerance.