This is like when kids start out competing to see who can be the quietest and end up screaming at each other, each to demand that they personally are the quietest. Whoever doesn’t join the competition usually ends up the unacknowledged winner.
I actually think that the only meaningful way to answer @lawrence_from_california 's question is to allow for negative interest, as @diegoalmendras seems to do. Saying “the least interesting species is this one I know nothing about, and nobody has ever taken much of an interest in, beyond the brief initial description” is both illogical (we don’t know about the species we don’t know about) and not that exciting. But saying, “this is the species I have the strongest disinterest in” is something many people could do, and in fact has led to some successful conversations on this forum before. One of many examples:
https://forum.inaturalist.org/t/whats-your-least-favorite-taxa-to-see-while-inatting/40583/3