I once had a TransStates Captain deny me the jumpseat for a 2 hour flight very early in the morning. He was a bigger guy, and that cockpit is pretty tight, and he was pretty much like "sorry I don't want anyone up here right now."

I respectfully said "thanks you guys have a nice trip" because it's his absolute right to refuse me a jumpseat for any reason (or no reason at all).

Jumpseating is a courtesy not a privilege.