In nullsec and lowsec, it's little posses of circus clowns in different colored uniforms, chasing each other about and creaming each other with pies having a jolly time. Sometimes fifty clowns will jump out of a dumpster and maul ten clowns, and that's OK. Sometimes eight hundred clowns will come galloping down the street and absolutely pulverize that poor gang of fifty clowns. But that's all fine, because out there everyone is required to wear a clown nose and all the other clowns already know what's going on.
But in hisec, there are hundreds of normal people who are not clowns at all. You might walk into a big room with two hundred people and not see any other clowns at all. But if you're from nullsec, sometimes there will be a few clowns in the room or in rooms nearby trying to pie you. This sounds like it could be fun as long as you don't accidentally pie a policeman or something.
To the nullsec clown's neverending frustration, it often turns out to be very different. Sometimes -dozens- of those normal people milling about are actively aiding and abetting the clowns that are hunting you. None of your own friends could ever be seen in normal garb or they would be ostracized, so you find yourself outnumbered and bewildered. You are surrounded by civilians whose faces you don't know, and if you ever get into a scrap with the enemy clown you'll probably get pushed about while he pies you and all his plainclothes friends knock your own pies out of your hand and jeer, putting on their own clown noses for fifteen minutes and running away.
If you bring enough friends you could probably come up with some tactics that might work sometimes, maybe bring some long sticks to push them away, but it takes a lot of dedication and you never know that they won't just get more plainclothes friends.