My parents have always pinched the life out of pennies when it comes to gas. Then they bought their first fuel injected car (1985 Accord) and after about a year of craptastic gas, it started idling low. Drove it to the nearest Honda dealer, 105 miles away, thinking it was something serious. They cleaned the injectors and told my parents to dig a little deeper in the change purse for gas, or they'd be back in another year.
They switched to Exxon, mainly to shut me up, but after I was grown and out of the house, they reverted to their old ways. They put the cheapest mess they can find in their new Hyundai right now. Where to find the cheapest gas is actually a topic of conversation with them. Makes me insane.