According to local reports, Avril's mic didn't work at the start of her show ... and she responded to the cavalcade of boos by yelling obscenities at crowd.
Rays rep Rick Vaughn tells TMZ, "The Rays demand profanity-free performances from all of our concert performers and we are extremely disappointed by the language used in last night's show. It is not consistent with the family-friendly atmosphere that Tropicana Field is known for."
Calls to Lavigne's rep were not returned.
UPDATE -- Several of our readers were in attendance last night and point out via our message board ... that while Avril did drop a few F-bombs, they weren't directed at anyone in particular. Her real fans, it seems, enjoyed the show just fine.