Well... I have two things...
Ok, so I was playing on this L4D server. Everyone was having a great time, then a complete noob with like, reading problems joins. For the first ten minutes he whinged about how long it was taking to 'donwload' the add-ons while we tried to communicate. Then he started asking how to get add-ons, so we told him to look at the blockland forms. BUT (here's the annoying part) he wouldn't listen and we all typed up around fifty messages say how to get them, and he still wouldn't listen???!!? Eventually he spawned and started acting all professional, so the host kicked him and he kept joining asking 'y u kcik?', but it also got funny. The host banned him after a while with a message saying how to get add-ons and how much of a noob he was.
The second time is when I was playing on PSProgrammers arcade gaming server and Tezuni can along and put a wall of blocks around the teleports so everyone was stuck at the spawn area. Just before Tezuni finished a noob joined and kept asking for admin so he could ban Tez, in a DED SERVER! So we all had to put up with admin requests and him asking us how to get admin. But he, like the noob above didn't get the message through and threatened to report Tez if he didn't remove his bricks. Tez eventually left, but rejoined and cleared his bricks and left again. But jesus wept you do find some right stupid people on the internet!
-edit- Actually, the most stupid thing I ever heard is:
do u ride kangae ros 2 skoo;l in astrailia
Translation- "Do you ride kangaroos to school in Australia?"
I replied "seriously, what stuff Have you been smoking? I gotta try some!"
Then he said "no rly do u????!??"
I said "If you even tried the RSPCA will kick you up the arse soooooo hard, you'll be the first person on Mars and without a rocket!"
He shut up after that, but said some not as stupid things later.
