Originally Posted by MuAT
Not to point anyone out specifically, but the thread asks "IN-FLIGHT" cockpit visits, which I would consider as when the plane is at altitudes > 50 feet.
Well, I was in the cockpit of a jet in Denver a while back. We were almost a mile high!
But seriously, post-flight cockpit visits aren't that hard to come by post-9/11, if you ask nicely. I usually try to do so when I have baggage waiting and am on a new airline or new aircraft type (for me), because I find it MUCH nicer than sitting at baggage claim.

That said, you have to read the situation... if the captain or FO is making 'I'm done and I want to go home' noises, it's probably best to get out of there.