Used to describe an
erection so hard that, if given the chance, a dingo (Australia's native
wild dog) would not be able to damage it.
Given the silliness of the statement, it's usually used to describe a non-sexual situation that a man would nonetheless enjoy
very much, such as a sporting event.
When the Cats won the 2007 AFL Grand Final, for the next week
I had a boner so hard a dingo couldn't have bitten through it. (boner, I've got a ... a dingo couldn't bite through - gotta use
the original here)