I was in France, and I discovered that one street lead to Ireland. I walked up to the border guard and asked about entry. She told me I’d need my passport and had to be off the streets by 3 am. When I went to reply, I found I could only speak in a terrible Lucky Charms esque accent. So I went back into France.
Later, I brought this up in a conversation with a co-worker. He told me the same thing had happened to him, and when he couldn’t speak without the leprechaun voice, they put a black mark in his passport. He was banned from the EU for ten years.