Jim CarreyIf you've been wondering what's been on Jim Carrey's mind since his recent split with Jenny McCarthy, the answer to that is "Boing."

Since April 24, Carrey has been tweeting the word up to 40 times day, using it to mean, well, just about anything. "I RRRefuse 2 define BOING!," he wrote on Tuesday. "1 day when you've given up your need 2 explain it and file it neatly away, 'BOING'... you will understand! }=^P"

The erratic tweets are a red flag for some fans of the actor, who is said to have battled depression and was the subject of a highly unflattering 2007 Radar magazine cover story about his behavior on the set of 'Number 23.' (Although as a hatchet job, the article falls short: Most of Carrey's co-workers who are quoted seem to have a great deal of respect for him.)