I don't get the "ham sandwich" in-jokes. Can someone explain it to me please?
It's a reference to the saying that a good presecutor can gat a grand jury to indict a ham sandwich - as in very little evidence is actually required.
As others have told you it is a common joke. When a grand jury indicts, they are just saying that there is sufficient evidence to believe that 1) a crime was committed, and 2) that the person being indicted did it. Doesnt have to be beyond a reasonable doubt. Just more likely than not. So its pretty easy standard to meet.