When fans first meet Turlough, he's a moody alien whose background is shrouded in mystery (not unlike the Doctor). He's working for a force of universal evil and is attempting to murder the titular Time Lord, all of which isn't particularly 'nice', but it is at least 'interesting'. Three stories later and that plot line ends... but they never get around to giving him another one. So he spends the better part of a season being a little bitchy and getting immediately locked up in every single place that they land before he finally gets fed up and in a last, desperate attempt to get attention, takes off his pants and goes home. To be fair, plenty of people make that mistake. But that still doesn't make it entertaining to watch.