What the achievement asks
Shoo a hundred Bloodfin Tadpoles in Nazjatar. Five points, account-wide, both factions.
The tadpoles are friendly, and shooing one is a single click. All hundred live in one place.
Why it has a bad reputation
Every tadpole you shoo spawns one or two hostile Bloodfin Sentries where it was standing. Bloodfin Village is already dense with murlocs and they respawn quickly, so on the ground the count becomes a running fight: you click, two things attack you, you kill them, you click again.
Done that way it is genuinely miserable, and that is where its reputation comes from.
Do it from the air
Stay mounted and the whole problem disappears. The sentries spawn, you are already gone.
The one obstacle is that clicking a tadpole normally requires dismounting. Monel-Hardened Stirrups remove that: they let you interact with things while mounted for two hours, which is far longer than you need. They are made by blacksmiths and are usually cheap on the auction house.
With flying and the stirrups, a hundred tadpoles takes about a quarter of an hour.
If you would rather not buy anything, a mount equipment barding stops you being dazed off your mount, which is the other thing that turns this into a fight. A druid in flight form has neither problem to begin with.
Two small settings that stop misclicks
Enemy nameplates sit right on top of the tadpoles in a crowd, and clicking one by mistake pulls the fight you were avoiding. Turning nameplates off for the duration helps more than it sounds.
The same goes for interacting on left click, which stops a stray click on a hostile murloc from starting combat.
While you are here, click one tadpole and wait: King Gakula is drawn out by exactly this, and he is one of the thirty-five rares in I Thought You Said They'd Be Rare?. You are standing in the right village anyway.