- Refusing to go bottom (especially when their character excels there)
- Constantly leaving after capping top - PLAY DEFENSE PEOPLE!
- Taking health bonuses on map only to return to base 20 seconds later
- Going for kills over taking a tower
- Initiating outside of your tower's range when group fighting
- Sticking with SR builds rather than the more reactive Dominion builds
- Diving the other team in the beginning fight at top. This is essentially a metagame within itself, there's so much that goes into winning that first battle. And nothing pisses me off more than winning the initial top, only to have everyone abandon the tower

This is the thing that most sets my blood pressure rising when I see it happen.

- Refusing to go bottom (especially when their character excels there)

A character like Heimer is EXCELLENT for the initial top fight. Sometimes it's beneficial for Heimer to go top while a melee sits on the bottom until it's been claimed, then switch.

- Constantly leaving after capping top - PLAY DEFENSE PEOPLE!

Not necessarily bad. If you can cap top fast enough, recall back, heal up and shop, you can often be back before the enemy. The trick is to not have EVERYONE do that... just in case.

- Taking health bonuses on map only to return to base 20 seconds later

Agreed

- Going for kills over taking a tower

Double agreed

- Initiating outside of your tower's range when group fighting

Triple agreed! In addition to that, you're not "defending" a point if you're fighting in lane.

- Sticking with SR builds rather than the more reactive Dominion builds

- Diving the other team in the beginning fight at top. This is essentially a metagame within itself, there's so much that goes into winning that first battle. And nothing pisses me off more than winning the initial top, only to have everyone abandon the tower

I always try to grab mid, so that way I can get to top last and pick off those that are low or people sitting outside of the melee range. The biggest issue I see at top is not enough focus fire. It shouldn't be 1v1 1v1 1v1 1v1, it should be 4v1 on each enemy until they're dead. (Focus on support and squishies first. Toss an exhaust on the tanky characters to keep them from coming to the aid of their teammates.)

But what if the health bonus is deep in enemy territory?

That sounds fine because it's an actual strategic move

If I have no injured allies nearby, I will frequently grab health relics in enemy territory just to deny the other guy. That is a valid strategy

Also, inb4 someone mentions aggro..

OT...

Trying to defend a point 1v4 while playing a champ who cannot possibly survive such a scenario for more than a few seconds. IF you can hold the enemy off for an appreciable amount of time (ie: distracting ALL of them from capping long enough/possibly killing one or two of them before your allies to show up), yes, by all means defend. If all you are going to do is die a second after the first two enemies engage you while the other two enemies start capping, your death has served no functional purpose.

Really, trying any engagement where you have no chance of surviving. The only time you should engage in a fight is when you know you can slow the enemy long enough for backup to arrive, do enough damage that the enemy has to retreat, or outright kill the enemy. Rushing in and dying without doing any of the above does not help. At all.

Pushing for a four cap when the fourth cap is heavily defended. The only time to try a for a fourth cap is when you know doing so isn't going to cause your team to collapse. I've lost many games where I was able to look back and pick out exactly the moment we gave momentum to the enemy by trying a four cap and losing.

Always defending a point by camping on the point. Works for some champs. Any champ with a jump will do better by camping in the brush near a point. Many other champs can defend by camping speed shrines (especially if the enemy has a ninja capper).

Not listening to pre-game chat. I cannot count the number of times I've been on a team where we've clearly decided who will go where only for somone to completely ignore the plan once the game starts (whether than be two going bot, two capping mid, someone ninja capping the enemy mid).

Not pushing minion waves. I love the Dominion minions. They are, in many instances, more helpful than some teammates.

Ignoring objectives. Just don't. Don't.

Trying to cap the enemy bot when two enemy are closing in on you. If you have pushed bot to the enemy point and/or killed the enemy bot, by all means cap the point. If you have done all that, but there are two or more of the enemy closing in on you (visibly charging towards you on-screen) fall back. It doesn't matter if you've already neutralized it. If you can't completely cap it before the charging enemies are on you, drop back. You already neutralized. They will have to kill time re-capping. And you forced two players to disengage from elsewhere. YOU HAVE DONE YOUR JOB. This relates to the "don't engage if you are just going to die" points, but I see this all the time for some reason. The enemy bot point is the easiest for them to take back. Getting yourself killed while trying to cap it for a few short seconds doesn't help at all.

Insisting Alistar go bot when he's clearly better at windmill.

Unless there is a teammate hurt, there is no reason NOT to take the health pack. It keeps a roaming enemy from getting it, and they respawn so stupidly fast.

Pushing a wave minions while the enemy team is dead, instead of running straight to the tower.

2 or more people capping the same point (certain exceptions apply.)

That windmill fight thing is too true. I just see champs with closing moves or jumps just go at the other team right when they show up and then get nuked down in .5 seconds. The whole point is to poke and prod until one of them can be wiped out in one volley. That or grab the tower if they're too busy to cancel your cap.

Picking Eve and getting Priscilla's Blessing...

Something that hasn't been mentioned is getting the mid relic. I've seen and been in many teams that simply ignore it all game long. Moreover, I've seen people always grabbing it when you completely dominate the enemy. This denies a resource useful for a possible comeback; in case your team goes for a fourth or fifth capture and ends up aced.

Finally, I prefer for somebody to take the mid relic when it's needed than to let it rot. Regardless, some champions benefit more from the shield and extra damage than others. I prefer auto-attackers and ability-spammers to take it, so that they can trigger the extra damage more often. A tank would benefit from the shield too.