This happens on swivel jaw vises all the time.  People often want to use them like a fixed jaw vise so they take a big hammer and beat the pin in place.  They really aren't as durable as a fixed jaw vise, but are incredibly handy when you have irregularly shaped object.

This post on Garage Journal has a lot of ideas for removing stuck pins from swivel jaw vises like this Yost.  It's usually some combination of heat and leverage:

http://www.garagejournal.com/forum/showpost.php?p=6187164&postcount=3834

On 2016-12-17 at 8:19 PM, John McPherson said:

And here is an example of a shop-built alternative for those of us not lucky enough to have already acquired such a beast.

 

Great Idea John Thanks