Damon in Cinderella swears because he doesn't care
Once the story progresses (which, once again, the full story is available on my quotev account @.captainpeanuts) you will find that Damon's character is very simple but very complicated emotionally due to traumas. This makes him a lot of different things and since he has a lot going for him in the field of emotions he doesn't care to keep himself proper to the max, especially since his father isn't there to regulate him.