S.G.
Ah yes, the independent-world revolves around me age! This is probably going to seem like it will take forever but it won't. You might get frustrated to the point that you want to give up-DON'T!
When your son ask for a glass of water in his normal way, get down to his level, look him face to face and repeat what he wants the way you want him to say it (calmly and with manners). IE:may I have some water please? Ask him to say it back to you in the same way you just said it. When he does, give him the water and when you hand it to him tell him that now he says thank you. Keep doing this till he starts getting the hang of it. And do you and anyone else in the house needs to ask him and each other they same way! Don't look at you son and tell him to put his shoes on, ask him to put his shoes on and say please and thank you after he has done it. And if he did it really fast, praise him for it!! Now after he starts getting the hang of asking politely, he will slip from time to time. When he asks for something but doesn't say please remind him by saying What do we say? (give him some hints if he is stuck) Don't tell him to say please because by doing this you aren't letting him think about the steps he needs to do to get what he wants. And if he forgets to say Thank You, same thing, ask him what he should say. When you know he has this down pat, you can start ignoring him when he doesn't say Please till he does and don't give him his cup (have it in your hand ready to give to him though) till he says Thank You. Remember, you don’t always have to give him what he wants just because he said please either. If you don’t want him to have a new toy or a piece of candy, then thank him for using his manners, but give him simple explanation and a no.
As for being loud and interrupting, it's the same thing. Teach him the difference between and 'inside' voice and 'outside' voice. If he starts yelling in the house or store, remind him to use his inside voice. If he does good at a store, praise him after you get in the car on how happy/proud it made you that he didn't get loud while you did your shopping.
As for interrupting, same thing as manners. Pause your conversation, get down to his level and tell him he has to wait his turn to speak. Then finish your conversation or find a break in it so you can let him talk. When you are ready for him to talk, let him know you are happy he waited his turn. Remind him it is just like being at the park and he has to wait his turn to go on the slide. Same thing when mommy is talking to someone. When you are sure he gets the hang of it, ignore him when he comes up to you and interrupts, don't even look at him. And if he starts to throw a fit, ignore it too! And when people look at you like you need to do something, look at them with a big smile and tell them that he is learning how to use his manners! I have a rule of thumb I use with my daughter and kids I babysit when I'm talking to a person or on the phone.....It must be an emergency to interrupt me, someone must be broken, burning or bleeding!
I did see that you and your boyfriend have a stressed relationship, make sure you two don't yell and argue in front of your son, it will send him mixed messages about how to treat others.
I know this may seem like a lot but it's not. In simple terms, treat your son like you want him to treat you! Remember to let him know how happy you are when he uses his manners too!!!
Good luck!!
S.
S.