I do not see all flirting outside a committed relationship cheating. If you're married, you've committed be be physically faithful to one person, but is that supposed to mean that you stifle all of your sexual energy outside the relationship? It would indeed be disrespectful to do so in front of your spouse if they are not secure with it, but flirting can be a harmless interaction that can brighten the day. I think most people know when an spicy interaction is just flirting, and if someone tried to take it further another could just politely decline and explain they are married. Temptation will always be around whether one flirts or not, no one needs to take it to an inappropriate place...
I feel about the same way, but in my opinion the bottom line is what the couple is comfortable with. I was in a long-term relationship with a girl and stated outright at the beginning that if she had feelings for another guy, that it was ok and she could just leave, no hard feelings at all, we can be friends or whatever, as long as she was honest and open about it. Later on we even agreed to have an open relationship. She could go flirt with and bang another guy if she really wanted to, as long as I knew her heart was with me.
Now the relationship is over, and she tells me that she had feelings for some other guy, like a year ago. That is definately cheating. To me, cheating is about being dishonest with your partner with another person, sexually or romantically.
Good rule of thumb for this situation: If you are sexually or romantically involved with another person outside of your relationship at any level (flirting, talking, or acting out) and you have to hide it from your partner, you are cheating. If your boundaries of what is considered cheating doesn't match up with your partners, you are with the wrong person.