Refers to the act of 'making-out with' or 'kissing' someone.
At the end of any disney cartoon the princess always gets her 'happily ever after' with the prince.
Due to the 'G' rated nature of Disney cartoons, the happy ending never involves more than a kiss with a handsome prince or hero (or maybe even an ogre).
The 'Disney Bang' refers to the act of 'doing the deed', Disney-style.
Wow, that guy is hot, I would love to Disney Bang him.