I despise the dingo. My hatred for this small, dog-like creature is not born from any wrong they've done me, not directly at least. Not for any threat they pose to me, quite the opposite in fact. Rather, my contempt is bred from familiarity.
The dingo is simply too prolific. They will appear in any biome that is not permanently covered in snow or salt water, and do so far more often than [FREQUENCY:5] would suggest. Almost always, to be specific regarding my experience. The result, for an adventurer, are repetitive encounters with cannon fodder that would be better served pitting you against deadlier, more exotic creatures.
Imagine an rpg with random encounters starts you off fighting a sewer rat that can be killed in one hit. Now imagine that every random encounter in that game is just that same rat, without any changes whatsoever. 1 hit, 1g, 1xp, all the way to the final boss. That is how the dingo do.
Removing dingoes has made the game much more enjoyable for me. I actually get to deal with things like entire prides of lions these days. Variety is the spice of life.
...Wait, this is a fort mode thread? In that case, keas, obviously. Same reason as the dingo actually, they appear everywhere and there's always a few already on map after I embark. I could deal with the thieving scum with wings bit if they just showed up less often. Removed them just like the dingo, never once regretted it.