GEST:
I have always heard the term 'Pincher Kiddies' - never come across 'Laddies, or the MacNicholas reference, but I always knew Paul O'Brien to be reliable. Cowley's book seems to bear out the 'Pincher'MacNicholas explanation, though in Hiberno-English, Pincher is given as a whinger, a petty, 'crabbid' individual.
Thanks for the question - it reminded me how good Cowley's book is - I'm going to re-read it.
Jim Carroll