That’s a tricky one! The worst hobbit I can think of is Lotho Sackville-Baggin, but even he wasn’t downright evi.
Ted Sandyman was pretty rotten as well.
Well, I do know of one who murdered his cousin over a piece of jewelry, but I don't think any Hobbit was purely evil. The Shire never even had a documented case of one Hobbit murdering another in it's entire history.
That means either they are unimaginably peaceful or ridiculously good asassins.
Otho and Lobelia were pretty unscrupulous, although they were nuisances rather than villains.
I would add that Lobelia went through a quite Dickensian change due to the events of the War of the Ring.