elastic asshole means: It is not necessary to prepare an asshole before you stick something in it.
(in Open Dictionary, added by Myah Gallagher)

What else does elastic asshole mean?

A rectum is a genital area of a male or female that has been “slammed” or fucked so often that it’s completely reamed out to a larger size than it could ever stretch. It is very useful in quick and easy anal actions.
(in Open Dictionary, added by Matilda Cochran)