I know we all know this, because we aren't fucking simpletons, but:

First of all, your father wasn't looking at your crotch like some kind of pervert. Humans have the capacity to notice strange things, and when they notice, they look at them to confirm. If you stuffed a pack of playing cards between your arse cheeks and then put on tight pants, people will notice there's a strange lump in your pants when they look at you. This isn't them staring at your arse, this is their ability to instantly glance and summarize a person's shape with the power of their primary and peripheral vision working together - and when there's an out of place lump, their brain instantly notices, draws attention to it and your father, rightly, said something about the fact you seemed to be hiding something in your pants.

Second of all - it's a party for 10 year old kids. At some stage you have made the following conscious choices before leaving that morning:
1) This will be a day and an event that I need to bring my artificial penis.
2) Despite claiming to be a man, this will be a day and event where some tight pants are appropriate.
3) Having claimed to be a man and still gone with pants that most men wouldn't wear to a children's party, and having installed your fake penis despite going to a children's party, you reviewed the lump in your pants so obvious that your own father instantly spotted it and said: "Yes, this what I want to show at a children's party"...

... The absolute fucking gall of you to stand there and accuse your father of inappropriate activity after this was your thought pattern is utterly disgusting.