Disable JOIN and PART Messages
Tools -> Options -> pick "IRC". Click the "Events..." button. Change the "joins", "parts", "quits", and "nicks" to your desired settings: "In Status" or "Hide" are good options.
To hide parts and joins on all channels, you can use
/set irc_conf_mode 1.
To hide parts and joins for a specific channel, you can right click the channel in your channel tree/tab, click Settings, then click Hide Join/Part Messages
Snak -> Preferences -> Channel, and uncheck "Parts" and "Joins".
/ignore -channels #channel * JOINS PARTS QUITS NICKS
/ignore #channel * CRAP