I'm with you - I can't stand add-ons that announce things to /p (or whatever). I've found that most PUG groups get pretty ornery when you have them enabled too. The last time I auto-updated my UI compilation, it re-set my announcements back to default (which, apparently, is 'announce everything').

Unfortunately, since I'm a considerate Tauren Fury Warrior, it announced to /p every time I interrupted a spell caster. So my PUG got spammed with "Oryx has just interrupted Dark Bolt" every CD. The comments ranged from, "Do you want a cookie?", to "Oh, look, we got paired with the interrupting cow!", to "Hey, at least he's using his interrupts".

Moral of the story: Turn all announcements off for PUGs.

Oh no! Not the interrupting c... MOOOOOOOOOO.

Ignore is your friend. Dont like it then you can ignore them, why should I turn off my addon that I like to appease someone I may never play with again? I have them set a certain away I don't want to have to modify them again until major patch day.

Long cooldowns are ok to announce, but interrupts should really be turned off. Not just for pugs, but everywhere. In a raid, if it's crucial that you interrupt, noones going to be checking the chat box for whether you got your interrupt off or not. I don't rage at pugs or anything, it doesn't overly bother me. And I cracked up at the rogue who had a macro binding /s Nutkick to his kick.

I'm with Draev here.

Announcing usage of tanking cooldowns is about the best thing you can do in -any- situation. I'm afraid your pet peeve here falls short of the actual good use that comes from announcing things. Now, if they announce something like "Interuptedz MOFO!" or "Look at me! I invincible!" I will agree. If it's something like "Guardian of Ancient Kings is up!", it's a wonderful way to let people know that you've used a cooldown.

I'm searching for a nice way to put it, but this is all I can think of: Deal with it. It harms nothing. It does not affect anything but your chat interface.

@Draev

Ignore is NOT the way to go with this one. Ignore does other things than just ignore the spam some tank (who is trying to do his best - and hence probably a decent tank), the most important thing it does here is it PREVENTS you from getting that tank through LFD again.
With tank shortages, and the silly queue times, the LAST thing you want to do is to ignore a decent tank.
Next I would ask - is it really appropriate to ignore the person who is controlling and leading your dungeon group? If he asks for cc from you, you wont hear or do it, he asks if you can kite/offheal/pause for 2 secs while he grabs a drink etc.....You WONT KNOW. This would make YOU the weak and emminently kickable link in that run then.
Still wanna ignore the tank? If not then just politely ask him to disable the addon - and give him 2 mins - then continue killing stuff. Simple.