When you start thinking about which MLB teams' fanbases have the filthiest mouths, there's a good chance a few cities instantly jump to mind. In fact, there's a good chance Philadelphia popped into your head. It did for me. But a new survey from Vegas Insider has found the most foul-mouthed fanbases in the MLB, and the top team might surprise you a little at first... and then it will make total sense. A new survey has found that Athletics fans are the most foul-mouthed in Major League Baseball. (Scott Marshall-Imagn Images) That team? Technically, a franchise that played in Philadelphia at one point, but is now in Sacramento limbonow in Sacramento limbo ahead of a move to Vegas: the Athletics. PHILLIES PLAYERS SCATTER AS RAT RUNS ALONG DUGOUT DURING ANOTHER LOSS, EXTENDING SEVEN-GAME SKID This was determined by combing through each of the 30 Big League teams' subreddits on social media platform Reddit and determining the percentage of comments that contained an expletive.…