Most Pathetic DnD Monster

[Flickerdart]

Of course, that depends on whether CR 1/10 monsters "are eight Challenge Ratings lower than the character's level", in which case you won't get any XP at all. It's a bit hard to interpret with fractional CRs.

A Human Commoner is CR 1/2. That goes down to 1/4, then 1/8, then 1/10, only 3 less.