Deteriorating into Texan

Here’s an article in the UK’s Daily Mail about an abandoned celebrity memoir from Jerry Hall. These things happen so in and of itself, this article isn’t that remarkable. However, I found this statement from one of Hall’s friends amusing:

“They seemed OK with her writing style but she couldn’t keep it up and it quickly deteriorated into Texan. And despite her typist’s best efforts to turn it into proper English, Jerry kept changing it back. It just didn’t really work.”

Just what does it mean to deteriorate into Texan?