when he has an underwear he just goes on himself

He’s probably confusing the feeling of the underwear with the feeling of a diaper. They feel so similar to him that he just goes. He knows that if he wets his diaper, it’ll just stay in the diaper, and you’ll change it. He may not be at the point yet where he can grasp the difference between underwear and a diaper. Try using white diapers and brightly colored underwear- skip the pullups until later on, as they’ll just confuse the heck out of him. As for him not going when he’s naked- him confusing diapers and underwear would again account for the lack of accidents. He knows not to pee on the floor, but maybe he doesn’t know that peeing in his underwear is kinda the same thing. Growing up is hard! :) At 2.5 he’s only barely into male-potty training age, so give him PLENTY of time. I’ve known boys who have taken until they were 4 to be COMPLETELY trained (and one is 5 and still in pull-ups at night). You’ll get him there! You’ll survive, and so will he. It’s all about body-mastery- it’s not necessarily a battle of wills all the time. I’ve also heard that little boys who pick out their underwear at the store and ‘pay for them’ (w/ your money, lol) and undergo the whole process of obtaining the underwear will feel like it’s more of a special thing and won’t want to soil them. I heard that on the radio- I don’t know anybody personally that has tried that method. GOOD LUCK :D