Dynamically generating the response would also allow you to gather chat statistics from big events not hosted on tmi.twitch.tv. I suggest avoiding literals with something like:
"PONG " + theServerAddress + "\r\n"
or
"PONG " + thePingMessage.substring(5) + "\r\n"
This is a good reference for IRC protocols: https://tools.ietf.org/html/rfc2812#section-3.7.3