Most characters only get a feat every three levels, which makes them pretty scarce for the majority of adventurers out there. So in turn, that makes them very valuable. They can be used to expand the arsenal in every regard; offense, defense, magic, and skills are just some of the realms that they can improve. However, if you are looking to make your character substantially worse here are some great feats.
Green Ear: Music to soothe the savage plant. Normally plants are immune to the magical effects of a bards music. Take this feat and that problem is a thing of the past. However, plant creatures do get a +5 (!) bonus to the Will save from the magic music. One of the prerequisites is 10 ranks in a perform skill, which means a character has to be at least 7th level to take this. I have hard time believing that a 7th level character can’t find a better feat to take. I suppose that in the right type of plant-based campaign this could be very useful, but I don’t know anyone who plays in a plant based campaign.
Eagle Claw Attack: The party confronts a locked door deep in the crypt of the evil lich. How will they surmount this obstacle? The wizard with Knock prepared, the lock picking thief, and the greatclub wielding barbarian all get out of the way for the monk who has mastered the art of the Eagle Claw Attack! With this awesome feat a character gets to add their wisdom bonus to damage against objects. Yes! Why would anyone take this feat? Then again, one of the requirements is Improved Sunder, so perhaps this character has a deep rooted hatred of objects and will take any advantage over them that they can get. A monk with this feat teamed with a barbarian who has Destructive Rage are clearly the bane of all inanimate objects.
Ki Blast: Keeping with the theme of all the great feats available to monks is Ki Blast, which allows the character to expend uses of stunning fist to throw a single, low powered ball of energy. It costs two uses of stunning fist to use the Ki Blast, which is not a very good ratio considering that stunning fist is actually very good. And what do you get for this trade? A single attack that does 3d6+wisdom modifier. It is a touch attack, which it has going for it, and the damage would be okay if the character was around 4th level. However, the requirements (Base Attack +8 and some other stuff) insure that this is a high level character, which really has no use for such a weak attack. I know that monks frequently struggle with ranged attacks, but there has to be a better option than this.