I wouldn’t “tell on him”, but I would have a serious conversation with him and stop inviting him to your house. You can hang out in public places or go to his house. Protect your sister, don’t just ignore it. It’ll happen again if you do.

You need to tell her. There are no good reasons why he would be doing that, and she deserves to know so she can protect herself and her possessions from someone creeping on her.

Help him snoop. Shit like that brings friends together.

Pretend you didn't see. Then move all your **** and sex toys to your cummerbund drawer in case he snoops in your underwear drawer. No one bothers to snoop in a cummerbund drawer!

Sounds like he just became your ex-best friend. People like that cannot be helped.

Gross. And you're actually considering enabling him? That's even worse

Ewww...dude. You need to tell your friend off AND tell your sister AND never invite him round again AND tell your family why. By ignoring it all, you are harming your sister and enabling his disgusting behaviour. No one wants to be friends with a pervert. Find a new friend and do the right thing ditching this one.

to me this heavily dependa on age cus if like younger then thirteen then no better person then the friend who cuaght them to set them on a better path. no brainer get others aware. if tell sister then well you gotta stop being their friend or later in life youd have to defends this action as to stop people trash talking him....you dont want that. if this is ilder then like 15.... well try for a new friend, cus they understand their action or are way to stupid

If you are younger teenagers then snooping in any females underwear draws for wank material is not unexpected nor unheard of. If you didn't have a sister you'd probably have caught him in your mum's underwear draw. On the bright side, at least you didn't catch him in HIS sisters or mums underwear... But you do need to have a chat with him about it. His hormones are getting in the way of his critical thinking. A simple, if awkward "mate, that's kinda creep behaviour? I know my sister is great and all but can you please just not disrespect her like that? It makes me feel icky." If he is embarrassed about it then he was just being a perfectly normal opportunistic teenage boy and you now have the educational opportunity to start discussing respect, boundaries and both of your behaviours towards women in general. The more respectful you both are, the more chance you have of finding and keeping girl friends in the future... If he kicks off about it or doesn't give a hoot then you don't actually want him as a friend because his behaviour WILL just get worse and you'll get tarred with the same brush. If you are both older than 14/15 then you need to just walk away because he really should know waaaay better by now. I hope you can use this to start actually talking with him about how to grow up into decent guys that end up as best men at each others weddings one day. There are women in your future who will appreciate it.

At the minimum you need to have a conversation with him