KIRK: Okay, did somebody put the “Kick me” sign on my back again?
(Lorelai and Rory are laughing.)
KIRK: It wasn’t funny last week, and it’s not funny now! I have asthma.
Asthma is a common long-term inflammatory disease of the airways of the lungs. Symptoms include coughing, wheezing, and shortness of breath, and episodes may occur several times a day, or a few times a week. There is no cure, but symptoms can be reduced by avoiding allergens and irritants (such as tobacco smoke), and using an inhaler with corticosteroids in it.
This is the first time in the show that we learn something about Kirk’s private life. It also shows us that Kirk is the town joke, and something of a whipping boy, so that Lorelai and Rory have no problems making fun of him in public.