Some things can be hard to believe, because, being indentified as male, one tends to see the civil sides of most men.
My advice is to generally be more observant of people in social situations, like parties, lunch hours etc. Especially in corners, corridors etc where they may assume not to be overheard.
Sometimes, venues, clubs and flats have their own geography of fear where some women feel a need to actively measure up space in between themselves and other people. If you have friends who may be subject to this, try asking. At the right occasion.
Especially a SO may be a good place to start if you want to hear general experiences. It can be as simple as "common sense knowledge" of whom you don't want to be stuck with smoking a cigarette on a balcony at a mutual friend's house party or family get-together.
To get to those figures, only ~2% of men need to be assholes.
This is why it's so important for the few men who see it happen to never let it go or brush it under the rug.
It's even considered the height of sophistication of many here to jump to conclusions about your politics and morality based on subcultural markers. I find this shockingly anti-intellectual and the whole atmosphere disingenuously hateful on both sides.
Now, I'm also bisexual, and I get that people want to be forward. It's called a mating signal for a reason, and that area is fraught with misunderstandings on both sides.
Well, I went in to a bar with my wife and a guy friend (of both of us). He's gay. We tried a relationship with him prior, but distance/timing meant it wouldnt. So, we were up visiting and going to an event, and he was the one showing us around town. Sooo, we walk in the bar, and it's a gay bar. No biggie. And then my friend starts showing me off like I'm his.... It took me a few moments to understand what was going on. And then I had upwards of 3 drinks offered in quick succession. One guy put his arms around my shoulders, while another grabbed my ass. It was a gay bar tending for what's called "Bears" (I'm also 6'5")... but there was some sort of soft-core underwear porn of skinny guys on huge monitors.
It was probably one of my worse experiences. And if anything, it was indicative of what women more routinely go through.
It sounds to me like your friend was being an asshole by a) not informing you of what sort of place you were going to, and b) by strongly signaling to the other folks there that you did know what type of place it was, and were a willing participant.
I'm not saying you weren't harassed, by the way, and I'm sorry you were being treated shittily. But it might be like getting splashed in the first three rows of a Sea World show - if you don't know it's coming, it's shitty, but some people go specifically for that experience.
Also to note, that I and my wife are bisexual and polyamorous (although with each other currently).
What did floor me was the signalling to other patrons that I was his in some capacity. Honestly I didn't have a clue what to really expect, as its very even keel at the local GLBT bar (mating signals are up front, simple no means no - probably due to being in a liberal college town).
And no, someone showing interest in me, be they male or female is cool :) Talking dirty? That's fine, until/if I say no more. I understand that and am flattered. Assaulting me... not cool. Liberal with words, and conservative with actions is usually how I handle mating signs.