I draw the line at kissing myself, and that's the quick light kissing not full-throttle, tongues tangoing stuff. But holding hands, arms around each other, quick kisses or hugs, even quick butt-squeezes and such, all strike me as okay.
Situation obviously comes into play, too. If you're at a couples/adults-only resort with your better half then a lot more is acceptable than if you're in a fast food restaurant or theatre (though making out in the darkness of a cinema is a time-honoured tradition that I am cool with as long you aren't sitting next to me).
Personally, though, I find that many of the posts I see about PDAs online are people griping about gay/lesbian couples and I wonder if they really feel the same about heterosexual couples doing it (in fact, I wonder what they get up to in public). There does seem to be a bit of a double standard among some people with regard to PDAs along the lines of "it's okay if it's a type of couple that I approve of but not for those other people".
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