Anal fisting and double anal fisting. I'm not a gaper for some reason though and can't prolapse. I have put a 17" dildo all the way up my butthole.

...so I'm definitely not your girl.  But I am really into fisting other people anally and the more someone can take the happier it makes me!  

In response to other comments on this thread, I wanted to mention that typically people who can handle extreme anal play have high levels of control over their sphincter and rectal muscles.  All that stuff is muscle.  Stretching yourself open is an act of muscular control.  So usually people who can handle extreme anal play do not have problems with BMs.  Quite the opposite: people who have high levels of control over their sphincters protect themselves from future problems with incontinence or hemorrhoids.  In essence, anal play is good for your anal health when done safely.  It's sort of like an exercise / sport wherein the better you get at it, the more muscular control you have, and the more likely you are to have a healthy experience with that part of your body.  Of course going too hard, too fast, or using drugs to aid with play can always cause problems and damage.  But healthy play is quite good for anal health!