Boil the macaroni until al dente. Do not overcook it. It will continue to cook a bit until cooled and will soak up the mayonnaise and soften. Drain the pasta well and place uncovered in the refrigerator until completely cooled. You can hurry the process by stirring it around a couple of times while it's cooling.
Peel and dice a carrot. Cook until barely tender but still crisp in a pan of boiling water. Drain well and cool in the fridge with the macaroni.
When the macaroni and carrots are completely chilled, remove from the refrigerator and add the flaked imitation crabmeat. Stir in the mayonnaise. Taste. Add salt and pepper until it suits your taste. I deliberately did not salt the pasta water because the mayonnaise adds a lot of saltiness. You can always add more but you can't remove it. The amount of salt and pepper you add is entirely per your liking.
Refrigerate until serving time. You will probably find that the macaroni has soaked up the mayonnaise and you may have to add more. Typically this style of macaroni sale is mayonnaise heavy. Again, this is entirely up to you.