There seem to be tons of debates about coed grappling, so I thought I'd add my two cents.
For the guys... (based on issues discussed on the interwebs)
2) If I'm training with a guy my size, he should be training exactly the same as he would with any guy his own height, weight and experience level. If I'm working with a much bigger or more experienced guy (which is usually the case), he should roll the same as he would with any guy my size and level (ie. don't just spazz and squash but do work your technique). If something hurts, I'll tap, end of story.
3) I do not care if you grab or push on the boobs (ie. harness grip) or other "questionable" areas. Don't be afraid to get in there and use your weight. This is BJJ, shit happens and is often necessary to finish a move. I'm not going to be all oh fuck u perv! any more than you would flip out on another guy for using the same techniques. I couldn't care less where your hands go while rolling or drilling. It's a close contact sport. If I was uncomfortable with having big sweaty guys all over me, I'd be doing tennis or something, and so would you. It's only awkward if you make it.
4) Please, for your sake and for those around you, wear a freakin cup. A really good one.
5) Don't be afraid to sub me and don't let me win just to make me feel good. If it's a friendly roll and you want to go lighter because you've got more experience and you think I'll learn from it, that's great. But don't give me special treatment or hesitate to apply submissions just because I'm a girl. If your technique won out, then I deserve to tap. That said, don't be THAT GUY who feels the need to go super hard and treat every roll like a competition, or who starts to spaz and use excessive strength just because you don't want to tap to a girl.
6) Men who refuse to train with women are douchebags who must be crushed. To those with religious reasons I ask, is it then entirely appropriate for you to be rolling around in those positions with anyone, including men? Probably not. So don't grapple in the first place. To those with jealous girlfriends...your relationship is that insecure? To those who worry about sexual issues: do you run into that problem with male partners? If not, then stop focusing so much on the anatomical differences and cultural taboos and fucking work your game. Also, get out of your parents' basement from time to time, then it won't seem like such a big deal when you get up close with a real live girl. To those who think it's not challenging enough or that they won't get anything out of it, your technique must be absolutely brilliant if you don't need to practice a bit more instead of powering through shit all the time. Besides, experienced female grapplers can probably kick your ass...sure you can't learn something from that? Lastly, to those with the momma said I can never hurt a girl attitude, grow up. If a girl has a problem being submitted, she shouldn't be grappling in the first place. If she's there to train like eveyone else, be respectful enough to train with her properly. Let go of the archaic attitudes and choke the hell out of her till she taps. No one who seriously trains BJJ is made of glass, so don't act like they are.
For the girls (inspired by talk with MMA instructor friend on recent disasters)...
2) The gym is not where one goes to look for a date. They have bars and websites for that. Not that it can't happen but that shouldn't be why you're there. Don't go out of your way to be the center of attention. It's inappropriate, not cute, and it's also rude to the majority of your training partners who are probably already in relationships and are not looking to be hit on during their exercise time.
3) Wear clothes that are sensible for training. Don't come in sporting skin-tight mini shorts and a freakin' bra with bunnies on it. MMA / board shorts and a t-shirt or rashguard are appropriate. Definitely wear stretch shorts or leggings as well because those babies will ride up and you don't want to start flashing tan lines.
4) Girls often walk into these types of gyms with more to prove, as do smaller men, but don't overcompensate by being a "badass" bitch. Be aggressive, absolutely, but don't do it in a dickish, loudmouth, over-the-top way because you're still going to get crushed and then you're just going to look like you totally deserved it. Chill out, enjoy yourself, learn and have fun.