Consider this situation:
Politician A "slings mud" at Politician B.
Politician B accuses Politician A of being a mudslinger
Politician A accuses B of being a hypocrite since accusing someone of being a mudslinger is a form of mudslinging
Politician B accuses A of accusing B of being a hypocrite only in order to sling mud so is begging the original accusation of mudslinging.
Politician A accuses Politician B of accusing A of accusing B of being a hypocrite only in order to sling mud so is begging the original accusation of mudslinging is still a form of mudslinging and therefore hypocritical.
(At step 4 Politician B could have instead said that accusing someone of hypocrisy is a form of mudslinging but this seems less plausible.)
So the argument goes like this:
A says ((B) is bad)
B says ((A says ((B) is bad) is bad)
A says ((B says ((A says ((B) is bad) is bad) is bad)
B says ((A says ((B says ((A says ((B) is bad) is bad) is bad) is bad)
A says ((B says (A says ((B says ((A says ((B) is bad) is bad) is bad) is bad) is bad
So what is happening here, that makes the moral concept of mudslinging (meaning as something that is bad) create a regress?