1. Ayan said, "Aisi halat ker dun ga k ankh utha ker nahi dekh sakegi", not once or twice but three times. Once to Sanjh on mobile and twice to Maya. Did he know beforehand that Maya was going to hide something in her clothes which eventually he would tear off to humiliate her? LOL. He said clearly "maut to bohot asan hogi tere liye", and what can be worse than death to a woman?
2. Maya never hinted that the key was in her clothes, or at least they didn't show that part. How can Ayan assume that it was in her dress. It was Maya's house, the key could be literally anywhere. He could break the door with force or search for something heavy to break in, but of all the options in the world, he jumped onto the conclusion that the key is in Maya's clothes.
3. When Samay tried to stop him, Ayan said, "Main chorun ga nahi is ko". Err, that not at all sound like a 'key search' to me.
4. The maximum benefit of doubt I can give to Ayan is that he might be trying to tear off her clothes only to humiliate her, but still how can we know that he was only tearing her clothes without taking pleasure out of it, and will not get carried away if Samay had not stopped him?
5. If the same scene happens in front of you, what would you think?
6. How will you differentiate between clothes ripping and a rape attempt? We only have the criminal's words for what exactly was in his mind, and the victim would definitely feel that he is going above and beyond.
I am not supporting Maya here, but she has not done anything to Ayan this much bad to deserve this behavior. She might have been a murderer but she has not murdered any loved one of Ayan so he had no right to be a vigilante.