When spamming in the single player, it disconnects you and saying "Disconnected by Server disconnect.spam"
Well... it's single player... not a server!
Proof:
http://youtu.be/DRUcaVQSFHY
Linked issues
Comments

Reproduce what? Sorry the noob question.
But is this the first issue ever reported of this bug?
It means that they could not get the result you got when they tried it on their game.

That is correct. That is not to say that your bug is invalid, as you have provided sufficient evidence to show its existence. I do not recall seeing any report similar to this one, and the search function does not reveal any duplicates, so it is very likely this is the first report for this bug.

Unable to reproduce either.
Please force a crash by pressing F3 + C for 10 seconds while ingame and attach the crash report here.
I can say that 100 lines in 4 seconds is enough to get me kicked for spam. Still got nothing in SP.
I'm sorry everyone but it's normal that in the Demo_World I get kicked and in the other worlds no? I've just been kicked in the Demo_World (tested it on other SP)
And when kicked, can't get the forced Crash (F3 + C)

You don't need to provide the crash when you're kicked; anytime will do. This report will provide us with more information about your computer system, software installation, etc.
But that's not the question. I just get kicked when spamming in the Minecraft Classic demo world in the version 1.4.6
Just in that world. It's that a bug of it or really nothing happens normally in that world? Confuse
This ticket has been marked as a duplicate of MC-14923, in favor of the better description/information provided.
Unable to reproduce.