Crash Test Tribble is a player title. It was awarded to players who participated in the first Tribble Test Weekend by copying their character(s) over to the Tribble Server and spent at least one hour on the test server.
The event ran between 14:00 Friday 19 March and 09:00 Monday 23 March 2010 (PST / GMT-8).
It is available in the 'Special Unlocks' section of the Zen Store if you are eligible for it.