MLS is right. “Displays of anger” is the problem. Kids read body language with the fluency of a native - 'cause they are. It’s all they have to go on. He knows, as evidenced by his laughter, that you’re not really angry in any way that’s meaningful for him. “Meaningful for him” meaning that it will affect him in a way he doesn’t like.
You can’t fake angry with a kid. And, frankly, they don’t care if you’re frustrated. They’re not so big on empathy at 18 months. It’s all about them.
Hair pulling is a hard one (sez the gal who just cut 16 inches off her hair), but it can be stopped. Basically, he sees this as a really fun game. Your job is to make it terribly dull. When he pulls, try not to make a big reaction. A simple, “Ouch! That hurts. You are not allowed to hurt other people.” will do. Of course, he’ll pull it again. Put him out of reach of your hair, saying again, “You are not allowed to hurt me.” Put him on the ground, in a swing, in his high chair, wherever. Then “ignore” him. (Obviously, don’t really ignore him, just don’t engage him or make eye contact.) When he fusses, ask “Are you ready to have fun and not hurt me?” He’ll of course say yes, and then pull your hair as you take him out of the chair. Lather, rinse, repeat. “I don’t want to play with people who hurt me.” Extend the time in the chair just slightly (maybe an extra minute).
Have a favorite toy close at hand, because one of the times, he won’t pull your hair, and you want to reinforce that toot sweet by having a fun activity to share together. Once he’s caught up in that, say something like, “Oh, we have so much fun together when you remember not to hurt me!”
This is, of course, a modified “time-out”, which works well with kids from about 15 months on. I don’t think little littles should be put in a room alone. I think that’s simply too scary for them, and increases fear rather than teaching consequences. I’d start room alone time-outs closer to 3 or 4. (Unless, of course, you’re so upset that you might hurt them, in which case, shut them in a safe room until you calm down.) But they need to keep hearing why they’re in the doghouse and what they can do to get out. AT NO TIME SHOULD YOU EVER TELL HIM THAT HE’S BAD, NAUGHTY OR A PAIN IN THE ASS! Never give him reason to believe that you’re withholding affection in an effort to control him. Always react quickly and consistently to his action (hair pulling) so he learns that he can control the doghouse-being-in. (If Skinner could use operant conditioning to train pigeons to play ping-pong, we can train our little monkeys!)
Obviously, it might help to have a friend our spouse available to entertain the other little un while this is all going on. But the good news is I wouldn’t expect the main teaching piece to last more than half an hour, with perhaps an occasional quickie reminder once a day for a week.
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Amazon Floozy Goddess** has a good tip for older kids, but I don’t think an 18 month old will make the connect between hair pulling and toys going away yet. But save that one for when he’s 3 or 4!

