Babbysitting the devil child!?

hahah ok ladies so im babysitting my friends 2 and a half year old i have a 20 month old who im quite strict with eg make him stay at the table till everyones finished says please and thank you is generally well behaved. My friend lets her son get away with murder he spits hits and will not sit at the table say thank you hes just a rude child! my husband cant stand him! but i feel for her and him as she a single mum and do kind of understand why she lets him do what he wants she doesn't always want to be the bad guy and she has to work full time! well today i offered to baby sit as her mum couldn't do it stupid me ahah! i have treated him the same way as i treat i do my own. he screamed at breakfast time and got down a hundred times i put him back in his he eventually stayed there but refused to eat anything he has shown my child how to spit and they both got in lots of trouble and i showed them to blow instead! its all i could think of lol i refused to give him anything without saying thank you which resulted in an almighty tantrum which i let him get on with i know his mum would have just giving in. but i wont as i dont want my son to think all these things are ok! am i being wrong by doing this? i cant stand horrible spoilt kids! i dont think the sun shines out my childs backside but im pretty strict! any advice would be great thanks