The prize for stating the bleeding obvious has to go to Ray Wilkins for this little nugget, back in the days when Channel 4 broadcast Italian football:
Somebody (sorry, I can't even remember who was playing, let alone the player) went down injured after a very, very high tackle. It was the typical, clichéd Latin histrionics thing with the guy rolling about and clutching himself. The commentator was rightly aghast at the nature of the challenge and wondered to his co-commentator if the player was seriously hurt. Cue Butch Wilkins in his usual laboured and monotonous drawl... "That's his shoulder, he's holding; that is."
Anyway, my vote has to go to Jamie Redknapp - some of the others mentioned in this thread might p*ss you off - but at least they manage to motivate the viewer/listener. Redknapp is just woeful. Has he ever said anything of consequence or with even a hint of controversy... ever?
Runners up would have to be Mark - right now I'm on the BBC and English but in half an hour, I'll be on Irish radio, so it's all change again - Lawrenson.
And, of course, Merson - if the guy was half as funny and half the charming rogue that he thinks he is, he'd nearly be likeable. But he's not. He's just a raw-mouthed idiot.
Best is Souness - but only when he's on RTE, where he's allowed to speak his mind. He's a different man on SKY.