Making out with friends is super fun. There is a reason we did it in high school, at parties, at summer camp, in the parking lot, and basically anywhere that wouldn't kick us out for lewd behavior. Now that we're older, there are other factors to consider that never concerned us back then. Things like the other person's feelings, for instance. Or unwanted transmissions. Or finding yourself in a "single white female" predicament, wondering what the hell happened and how you landed up in this position (again). And, of course, whenever you cross that line with a friend, you run the risk of ruining the friendship. Before you take that leap into your girl friend's toned and welcoming arms, there are a few things to consider.
We all have good-looking straight friends, some of them single, some of them flirtatious enough to set your mind wandering. Straight girls can be the perfect make-out buddy. First of all, you don't have to worry about them wanting an actual relationship. Secondly, the odds of you getting down and dirty are slim, assuming she is genuinely straight, so you have pretty much zero pressure to take it anywhere other than "light". Go out dancing, buy her a drink, and have some fun. I recommend staying away from the "kissing another girl to catch the guy's attention" route, mostly because I think it's kind of degrading and you don't want to open your eyes to see her staring at some dude across the bar. Take it outside or in a dark corner, and it will be more enjoyable for you both.
Also, I've found that weddings are a great venue for some smooching. Everyone's happy, loopy (aka inebriated), touchy-feely, and it just seems so fitting to kiss the ones you love (especially the ones with nice racks that have always caught your eye). The other benefit of weddings is that they keep it from evolving into a habit, which means no attachment issues on either end. Take stock of the cute female revelers, whether they be straight, gay, or bi, and make it happen. Everyone looks good at weddings, including you, and nothing is sexier than confidence combined with a happy smile.
Now, as far as your straight friends who have boyfriends go, the water is a little murkier. We're all adults, and if we're all consenting adults, then a little kissing here and there should not be a problem. Just put the emphasis on a "little" and make sure the boyfriend is in on it, as in he knows and gave the go ahead, not physically "in on it." (That's another story altogether.) With permission and boundaries, this can be a fun, extracurricular activity.
Note: If she starts initiating secret liaisons or if she wants more than a few make out sessions, you should reassess the situation. No one wants to be a homewrecker.
Having a gay girl friend with benefits can be beneficial to both parties. The key is to establish some rules and regulations at the onset, in order to prevent future heart bruising. Also, and this applies to any friend you want to get fresh with, keep your eyes peeled for tell-tale warning signs. Is she texting you first thing in the morning and multiple times throughout the day? Is she keeping the hookups on the down-low? I mean, she doesn't need to tell her family for goodness sake, but if she's not telling anyone -- not even her best friend -- this is a bad sign. Has she dropped out of the dating scene completely? Key words or phrases may pop up; listen and heed. I mean, I love kissing cute girls just as much as the next gal, but I knew I was playing with fire when some red hot words burned and flashed through my lust.
"Future," "can't live without you," "life changing," "two-timing b*tch," or one of my all-time favorites, "sorry about the emotional Mind-F**k, but... ", "I let myself in" (really? How the heck did you get my key?), "Do you feel the same?" Listen, and take note. The thing is, we have gut instincts for a reason. Obey them and you will save yourself some heartache and precious energy. I have experienced firsthand just how fun it can be to make out with your friends, and these girls remain my friends to this day. Establish boundaries and have some fun!