We've bought some absolute shite over the years, many of the worst idiots identified in this thread. Going back further, I'd add the likes of Paul Upfield, Steve Worthington, Shane Kelly and the slow, useless block-skulled clown five eighth from 1988 Shoeboxhead Robinson.
But for me the worst ever was Bronko DJura. Here's the scenario: It's the dog end of 1986 and we've underachieved desperately after the heartbreak of '85. Souths on the other hand have had their best season in years, forged on the shrewd kicking game of Neil Baker. Rumours start to circulate about Saints being in the market for an un-named kicking back from Souths. Obviously we're all thinking Baker. But it turns out to be bit part Rabbitohs reserve grade utility D'Jura. Saints failed to crack the semis for next five years, and for each of those miserable seasons D'Jura was a fixture, failing at fullback, centre, five eighth and dummy half. Slow, dim-witted and with a half dazed look he was the living embodiment of an era in which we were the sort of joke that Souths and the Scum are today. He should have his own plaque on the Legends Walk as a warning of what depths it's possible to sink to.