No way! If her spouse gets hung up on a chaste peck between friends, he needs help.
Not cheating, but I’d stick to the cheek or forehead, just to be safe.
As a married man, I’d be uncomfortable with anything on the lips. Cheek or forehead is OK.
Why would you want to kiss your best friends wife on the lips? Isn’t that just reserved for your partner and the dog?
The husband would feel better if you told him “I used to kiss her on the lips, but it’s all over now.”
relationships and attitudes about them vary from person to person. I wouldn’t consider a kiss on the forehead or cheek inappropriate. I have a close long time lady friend and although we never dated there were definitely sparks years ago and romantic feelings for both of us. When we see each other every few months there is usually a kiss on the cheek.
I think if both partners in a relationship are open about there friendships and talk about what is appropriate or acceptable a chaste kiss on the mouth is okay as well.
My attitude was , if your male friends know your in a relationship then they should accept me as a friend as well. If they don’t seem interested in a friendship with me then I’d question their motives.
If chaste, not chased, then all is well.
Do you lust after her, in your heart?
Do you dream of her, later? And I do mean dream.
If yes to either, either knock it off, or both of you get divorced first.
The wife and I are friends; the husband and I are, I don’t know, friends in law. And we stopped kissing in greeting even before she got married.
I used myself and my friend only as an example. The poll is mostly about attitudes about platonic kissing.
I do this with some friends. Kisses on the lips are OK in my book (no tongue!). In fact, the person who does it to me most consistently is my wife’s best friend.
Then myself and a lot of other people need help. I certainly wouldn’t declare that my wife had been cheating on me, but I would be upset. Likely pretty upset.
A Kiss on the lips has more sexual connotation, and is therefore inappropriate. A kiss on the cheek is totally fine as long as you don’t then lay your head on her shoulder and snuggle in.
I would be taken aback by the number of “inappropriate” responses in this thread if not for the fact that I’ve been participating in relationship threads on this board for the last five years. 
Everyone is allowed to have their own personal boundaries, of course, but to define someone else’s kissing on the forehead/cheek/lips when it falls within the context of their friendly relationship is just ridiculous to me. One of my closest friends is someone who always greets me and says goodbye with a kiss on the lips. But she does that with all of her good friends. When I was married, this happened in front of my wife, and TO my wife. There has never been a spontaneous bout of tongue-wrestling as a result, believe it or not. And I have a number of other female friends with whom I share cheek-kisses, including the infamous European double-cheek kiss with a squeeze (which, by the way, has accidentally led to a kiss on the lips twice, I think). Despite these violations of appropriateness, which have happened in front of her husband, he continues to consider me one of his best friends, still plays tennis with me, and – as far as I’m aware – is not secretly plotting my doom.
Am I suggesting I’m the model for appropriateness? Well, yes – but that has nothing to do with this thread. I think appropriateness is all about what is expected and acceptable to all parties involved (including present or non-present significant others of either party), and no one else gets to tell them any differently.
I just personally find kissing anyone you’re not in a sexual relationship of some sort with, on the lips, odd. Kiss on the cheek for a friend? No worries, that’s normal. Kiss on the forehead for a dear friend or small child is okay.
Personally, I’d rather have you give my wife a pat on the ass than a kiss on the lips.
But whatever works for you.
I voted “cheating” based on the clarification from the OP that cheating = inappropriate.
This is why the French invented the double-cheek air kiss. No chance of a mis-communication with it.
I think all the kissing is really just asking for trouble. Even if it is perfectly innocent people can definitely take it the wrong way.
I voted for the “open mouth is cheating” option, but what I really meant is something closer to “slipping some tongue is very inappropriate”.
Nothing, and I do mean NOTHING, is cheating except insofar as you have established what the rules are.
Except deliberately misleading someone. Anything you are hiding from the other person because you KNOW they would blow a gasket if they knew is something you’re doing behind the other person’s back, knowing it would hurt them. If you know that, you shouldn’t oughta be doing that.