A few days ago, at the most ridiculous Shabbos table, someone mentioned that she didn't know what 'the metascruple' is. The circumstances then did not allow we to explain, but here, where you all come to hear me hold forth, I figured I can do this topic justice.
We encounter all sorts of things in life (e.g. pork, MOTOGs, rainbows, etc.) Scruples are principles that help us relate to the things we encounter (don't eat it, don't talk to it, say some Hebrew words but don't stare at it).
We encounter all sorts of scruples when going through life. A frum Jew, who is subject to a constant barrage of scruples, may find him or herself with a bunch of contradictory scruples (the tefillin daters) or lots of scruples which he or she cannot implement (e.g. stay up all Thursday night AND go on mivtzoim all Friday afternoon AND farbreng Friday night AND say tehillim Shabbos mevorchim morning AND learn Chassidus before davening AND daven b'avoda AND farbreng Shabbos afternoon AND go on tahalucha AND learn Chitas Rambam AND meseches Sota [if it happens to be shabbos mevorchim Iyar]) or one especially difficult-to-implement scruple which he or she breaks regularly (e.g. not listening to non-Jewish music, not talking to MOTOGs, and not killing millions of unborn and unconceived children).
A metascruple is a principle that allows us relate to the scruples we encounter. "I'll act the way I was raised," WWJD, and "let me call my mashpia" are all examples of metascruples. I think the Rebbe believed that for people coming closer to Judaism, a good metascruple would be not worry too much about the consistency between one's scruples; rather one should focus on making as many of one's actions as possible fit with as many of the Torah's scruples as possible.
If one is completely metascupleless, a common affliction is guilt: without a metascruple to sort through your different scruples, how can you avoid breaking some of them now and then?
My personal metascruple, which I often inaccurately refer to as 'the metascruple' is good at eliminating guilt. It is: If you will have a scruple, then implement it; if you won't implement a scruple, then don't have it.