"I picked up a good tip at the weekend. If you purposely tune your guitar down a semitone, it buggers up all the would be joiners in ¦¬]"

We have a trad guy at our club who has a dislike for players, and pitches his songs usually in G# or C# to try to 'throw' the players. We take no notice and play along in the chosen key - it's good practice, you know, certainly for mandolin :-)