When i go to my.knees to his.****.
When you've decided that the person your flirting with is some one you are going to take to the bed and have an intimate time with, then the flirting stops.
When you took my hand and held it tight between your legs as I nibbled on your ear. Yes, I do believe that's when it went from flirting to something more than flirting - although I wouldn't call that sex .. :)
When you have sex
I ignored it saying it was just me being silly until they told me they were getting married...Never trust a friend as far as you can throw them...in matters of the heart.
I would say that when he's got his hand in your knickers... there was some point where it stopped being "just flirting".
different ppl have different threshold regarding that , so its difficult to tell in general ....nice question