https://www.answers.com/youth-sports/How_to_get_your_dad_to_let_you_wear_girls_underwear_if_your_a_12yaer_boy
How to get your dad to let you wear girls underwear if your a 12yaer boy? - Answers
If you have to or want to then just don't tell him. But I don't recommend a 12 year old to wear girls underwear if you are a boy.