As a performer, "You're A Mean One Mr. Grinch" is the easiest song to perform during the Christmas season because the chord progression practically plays itself and if you forget the lyrics all you have to do is make up insults and make them rhyme.

You're an asshole, Mister Grinch.
You're a sack of human dirt.
You're as smelly as a dung heap in a mouldy goat filled yurt, Mister Grinch!
You're a collection of worms and chicken guts compacted in an over-stuffed old shirt.