Seemingly deliberate habits. Do you really mean to chew your food the way you do? Laugh at the stuff that makes you laugh? Sing in a way that makes dogs in the next neighborhood squeal in pain? Probably not. And you know what? It might be the case that your sweetheart isn't deliberately trying to irritate you either. Maybe he's not aware of the fact that his snoring makes you want to poison him in his sleep. Maybe his nail-biting has nothing to do with you. Maybe you need to stop taking everything he does so personally. Once you do that, consider whether or not you can live with the annoyance. If not, feel free to gently enlighten him about the fact that he hums when he reads and that said humming makes it difficult for you to concentrate on watching American Idol. He probably has no idea.
Flirting. There's nothing wrong with a little how-do-you-do, but if your partner's flirting has crossed the line from innocent friendliness to outright irritation, Psychology Today recommends that you "look beyond your own hurt feelings and ask yourself what your partner is looking for." It might be the case that he wants more quality time, less nagging, more help with household chores, or just a little bit more fun. Take an honest look at what you are and aren't giving each other and do your best to bring that back to the relationship.
Criticism. Communication is good. Too much communication is bad. And yes, it's possible to communicate too much. If you feel that you and your partner are talking and talking, but all that's coming out is criticism and complaining, interrupt things. Add some playfulness or a joke or an overtly affectionate move to the interaction. The goal in doing so isn't to shut down the conversation, but to make it more constructive and a little kinder. It might just be that you'll say less, but hear (and love) each other a little more in the long run.