irc.perl.org servers all run a thing called bopm - the blitzed open proxy
monitor - which checks connecting hosts for shit like not being on blacklists
(dnsbls mostly) and checks a decent number of common ports for open proxies.
It does this by connecting to various ports, attempting to loopback to its
own ircd, and if it gets something that looks like said ircd it 24 hour K-line's
the host.

Of course, if you happen to run your client from the same box the ircd's on,
and you haven't exempted it from the scanning, then as soon as it tries 6667,
well, the CONNECT line that would make a proxy connect is ignored but that's
ok because it's already your ircd anyway so that's a POSITIVE IDENTIFICATION
OF AN OPEN PROXY.

And just like that, I K-lined myself and the rest of shadowcat off the IRC
server I'd just got halfway through configuring.

So yeah, don't do that ...