Hi M.,
For starters I am no expert but I have 4 children and I watch 4 more, so I have to be very consistent on discipline around here. I have a 16 yr old, 7 yr old, 3 1/2 yr old and a 15 month old. Then I watch a 2 1/2 yr old, 17 month old, 14 month old and a 1 yr old.
The one thing I use consistently in my daycare is the corner or time out whichever you want to call it. The 17 month old that I watch has the problem of pushing people down, hitting, and throwing toys, for each of these he is sent to the corner and told NO and whatever he did. For right now it's more about letting him know that this will not happen no matter what. And just like your son he doesn't quite know what the purpose is but when I say A go to the corner he know where it is and starts to cry because he did something wrong. So be consistent if you are gonna sned him to the corner for doing these types of things then you have to do it every time, no matter where you are, what you are doing or who is there.
On another note make sure your son can tell the difference between your "I live you" voice, and "I am disappointed in you" voice. So for instance when your son pinches you, tell him NO in a stern deeper voice and then tell hime to go to the corner (or at this point help him get there), let him know that pinching is not nice and he has to sit in the corner. Now here is the part that I don't agree with on time out, when you send a child to time out they are supposed to stay there 1 minute per their age so if they are 1 it would be one minute. In a 1 yr old they don't even understand the concept of a minute, but what they do understand is that what was going on around him before he went to the corner is still going on while he is in the corner. So he sees that he is missing. Letting him sit there for 3 or 4 minutes is not going to hurt him. So put him in the corner let him know you were not nice to mommy and when this goes off you can get up. If he gets out put him back. Make him stay there.
I had 1 of my daycare kids last Saturday night and we were eating dinner at a restaurant and he started messing with the blinds. I asked him if he needed me to find a corner and he looked like a deer in headlights. He immediately let go of the binds and didn't touch them again.
Your son doesn't realizre that him pinching you hurts but what he will realize is that if he does mean things he has to sit in the corner. And that is not very fun for him.
Also when you talk to him talk in clear words and sentences. And make sure you are at eye level with him and explain what he did wrong and let him know that he can get out and give him hug and a kiss. Then go on about your meery way.
Timeout is effective if you use consistently.