A colleague on my Gnat course popped into a shop in Llangefni. His haircut and general demeanour marked him out as an RAF officer, so a few of the local viet taff switched into their druidic tongue and started discussing what they thought about their visitor, the RAF and England in general...
Mistake.
Chum came from South Wales and spoke fluent Welsh. So after a few minutes he went up to the counter to pay, thanked the ignorant oafs for providing him with some amusement and advised them that they wouldn't be welcome south of the Menai until they'd learned some manners!