(I'm a bit more experienced with this one, as I own a pixelmon server myself.)

1) The beggers.

Now, while there are always beggers on every type of server, pixelmon ones are the worst. They'll ask for anything - staff, op, legendarys, money, masterballs, pokemon! It's horrible, I can't last 5 minutes in chat without someone begging, despite a "no begging" rule. I mean, asking for something reasonable once is ok, but the begging starts when they ask over and over and over again.

Please stop.

2) The 11 year olds.

Bit of a vauge group, but this is anyone who is under 13 really. They don't understand how a server works, build the ugliest houses, talk with no grammar or spelling checks, think that everyone is their slaves, nearly always beg, type in full caps and more. Now, not all young minecrafters act like this (I didn't when I was 12), but honestly, the majority do.

3) The loyal players.

These are those people that have an ontime larger than the head staff, have bases hundreds of blocks squared, have PCs filled with legendaries and shinies, know the owner's full name (and probably adress), can answer any question about the server and have hundreds of forum posts, yet usually aren't staff.

They're awesome.

4) The donator.

Honestly, this isn't as bad as on factions or prison servers, but they're still annoying. One day, you decide to donate to your favourite server, and as you go to the donation store you see a top donator box. And BAM! Your generous mood disappears. Why? Because this person has donated over $500. Most of the time these people have jobs, but for real. How can you spend that much on a server.

But hey, they're useful.

5) The breeders.

The people who obsess over ivs, have hundreds of ranch blocks, millions of eggs and thousands of dittos.