The tag alias #69069 slapping_own_butt -> auto_butt_slap is pending approval.
Reason: More in line with other auto tags.
Topic: Tag alias: slapping_own_butt -> auto_butt_slap
Posted under Tag Alias and Implication Suggestions
I think the difference is that "autofellatio" and "autocunnilingus" are actual terms that exist, while this is just muddying the waters. Very few, if any, people are going to see a character slap themselves on the butt and think of tagging it with "auto_butt_slap" instead of the current tag. I personally think it would be a better idea to imply both the current tag and you suggestion to "self_spank", since that's a much more concise way to describe the action.
As a side note, "Autobutt" sounds like something the Decepticons would call the Autobots in the original G1 cartoon.