C.P.
I dont know if a time out is going to work. It sounds like temper tantrum to me. At 18 months he doesn't have any impulse control yet so whatever comes into his head he is going to do because he doesn't yet have that little voice in his head that tells him which things not to do. And if you put his in his crib for time out he's going to connect his crib with punishment and will get upset at bedtime and nap time because he'll think everytime you put him in his crib he's doing something wrong. I would talk to his pediatrician next time you take him in. If they are temper tantrums they are only going to get worse with the more attention he gets for it. If you ignore him it will stop. My nephew did the same thing. I started ignoring him when he did it at my house. Now he only throws tantrums at his home or grandparents but not at my house, because he knows he can't get attention for it here. hope this helps.