For some time now I have struggled to give an abbreviated version of what I do.  When “I’m a lawyer” elicits the question, “What sort of law do you practice?” I find that there is no short, layman’s-terms explanation of structured finance that doesn’t put people to sleep.  Recently I have resorted to saying, “I do the sort of stuff that caused the credit crunch,” but some people, on hearing that, start backing away in…