At what point in the relationship are you comfortable to openly fart?

I remember with my first lover, it'd been over a year of 'radio silence', then during a bout of sex one slipped out. I blurted out "I did a botty burp!" She almost pissed herself laughing. Still, she was not comfortable reciprocating. When a few weeks later, in same situation, one of hers slipped out, she declared 'I'm going back to Brisbane!'.