In article 2013031520590123397-nospam@nospamcom, eastender wrote:
This pictu

http://www.flickr.com/photos/49435266@N05/8560821612

is of my son's lunch jar. He had little lunch today because no one at
his school could unscrew the top. We've tried and cannot do it - if I
had a large enough vice probably but we can't grip the body and get a
purchase on the top. I've tried a rubber jar opener.

Looking at another one (we brought them back from the US) the lid has a
large plastic washer/seal which may have got jammed. My wife put the
lid on this morning but she is not especially strong.

Any ideas how to get the top off and the lunch out?

Someone's got to say it - angle grinder.

More seriously, was the lunch warm when it was put in and created a partial
vacuum when it cooled? In which case put it in hot water for a while?
(Might even help if that wasn't the original problem.)