This was one of the more disapproving questions, i.e. one obviously about Other Girls and not about the questioners, so I will proceed carefully. For one thing, many girls and guys do indeed have "brother-sister" relationships which they both acknowledge. Sometimes when a girl says "he's like my brother", the para-brother is all smiles and quick to assure any other pretty girl around that "she's like my sister."
He's only like your brother if he thinks you are like his sister. And unless he has actually told you (or other women) that you are like a sister, you aren't. You are a potential mate. (Oh, how exciting to write the words "potential mate" at 9:36 in the morning. That should wake everyone up.)
And, therefore, if you do not have a scrap of romantic interest in some guy, it is not kind to shriek "Snuggles!" and throw yourself in his arms unless he thinks you are "like his sister" or his heart is covered in rawhide. It is also not kind to wander about him in a state of partial undress or, if he has no wife or girlfriend, to pour your heart out to him about your man troubles.
Because I can hear Alisha's shrieks of protest from afar, I will acknowledge that the entertainment community is incredibly huggy and kissy and snuggly and, for all I know, whole casts of musicals cuddle down under a duvet together to watch "A Star is Born" on TV. But I don't think this is such a great idea for anyone else. I realize that I am ruining the fun for various Catholic guys who think actually it would be great to cuddle with a whole lot of girls under a duvet watching TV, as long as another guy didn't touch them by accident, but too bad. I live in the UK, where no guy but my husband ever hugs me, so I have no time for your polygamous duvet yearnings.
In short, just because a girl thinks a guy is (or should be) as sexless as a muppet doesn't mean he actually is, so take care and have some respect. This does not mean creeping about in fear because some innocent soul will be damned to hell if he sees your knees. It mostly means not rubbing up against a guy like a cat and then dashing his erotic hopes by saying, "Oh, but you're like my brother!"
For the record, I have a super-formal Anglo-Saxon family, and the adults hug about twice a year. If I laid my head on one of my brothers' shoulders, he would think there was something seriously wrong with me. Meanwhile, if in close quarters and scantily clad, we wrap ourselves in long Afghan blankets crocheted by my mother which trail behind us like the more dramatic togas. I never got why brother = super-casual affectionate behaviour, but I realize families are different.