Who: The guy who, when singing Jingle Bells, belts out “Ha Ha HAH!” right after the “laughing all the way” line.
Why: He’s usually part of a choral or a cappella group or maybe just a bloke who’s had one too many at an office holiday party. Regardless, he thinks it the height of seasonal joviality and outright hilarity to punctuate a simple line in a yuletide favorite with some boisterous pretend mirth as if anyone hearing the song couldn’t understand the concept of someone “laughing all the way” (which isn’t, by the way, literally “laughing all the way” like some maniac in a Napoleon XIV song but more of an illustration of how joyous the sleigh ride actually is). He doesn’t think it necessary to pepper other lines from the song with extraneous sound effects. I mean, there’s no horse whinny or bobtail growl (I will admit to being somewhat vague on what the other lyrics are but, still, the point is made). Basically, his desire to be the center of attention supplants any regard for his audience, fellow singers or musical sensibilities.
How I justify it: He’s just some grandstanding doofus who deserves coal in stocking and a damn good thrashing by the Krampus.