What is the origin of the phrase "Don't mess with Texas"?

"Don't Mess with Texas" is a slogan for a campaign aimed at reducing littering on Texas roadways by the Texas Department of Transportation (TxDOT). In 1985 the TxDOT asked Mike Blair and Tim McClure of GSD&M to create a slogan for an anti-littering campaign. At the time the state of Texas spent about $20 million annually to clean litter from highways. McClure said that "bubbas in pickup trucks" who regularly littered beer cans and other items out of vehicle windows and ordinary Texans who believed that littering was a "God-given right" were targets of the advertising campaign. McClure said that he created the slogan when he saw garbage while walking near his house. Emanuella Grinberg of CNN said that McClure had "an eleventh-hour 'aha' moment" when, after looking at the trash, he recalled his mother telling him that his room was messy.

Source: Wikipedia