Simply, its where one places an apple pie (Favorably, the Kipling variety is used) over the receiving chaps anus, and begins anal intercourse with the said arsehole essentially crumbling up the apple pie over the
rectal passage. The end resulting jizzy pooey
apple crumble is then shared, A delacasy in certain parts of the world.
The act is not strictly kept to the gay community however, no known
documentation of women trying Bert's Apple Crumble have been found.