Back in the days of world exploration and navy's on wooden boats, a Scottish doctor discovered that due to a lack of vitamin C, sailors were dying of scurvy. He found that lemon juice helped. The American sailors laughed, so they kept dying. Then the British sailors found that lime juice was much better. The American sailors eventually moved up to lemons, didn't die out as much, and called the British limeys as an insult.
But the Americans were slow on the uptake and stuck with Lemons.
So yeah, the odd nut case around here likes to use Limeys, thinking it's an insult, but they're just lemons. They have a low IQ.