Basically shortened for 'on the sly' basically a way of describing somebody doing what ever slyly or by doing something quite cool.
Popular around the north west of England
I ont is short for I don't care. So you can yell it out loud when you dont care about somthin and the people around won't understand..
Mrs. K is teaching a long long lesson and you and the kids around you don't care at all. In the middle of her sentence you say I on't!!! Out loud. It covers up I don't care so you wont get in trouble.
Jerry is scared as hell to figt Kevin and is making up a bunch of excuses not to fight... In the middle of his lame ass excuses say I ONT!!