A special type of orgasm involving a Mc Donalds food dish and mass pleasure.
Ex. Combining a Mc Chicken with a double Cheeseburger = a Mcgasm in your mouth.
Steve: hey man are you OK? You've been chewing that chunk of your Big Mac for five minutes now.
Bob: *swallows* Yea I'm fine its just that big mac.... its so good it was causing multiple Mcgasms in my mouth.