Scariest border crossing you've experienced while traveling?

I took a bus from Bulgaria to Istanbul, Turkey. I had dual US/UK citizenship, and my UK passport was about to expire in 6 weeks. I knew that both countries would allow me to enter with a passport valid for <6 months, but the bus driver kept saying things like, "Oh I don't know mate, they don't let you in the country with a passport like that."<br><br>He said he'd let me off at the Turkish side of the border and I'd have to walk back into Bulgaria and take the next bus (and pay another fare.) This was the middle of nowhere, with very basic border crossing stations. There was no way I was going to be able to walk back into Bulgaria.<br><br>So I used my US passport and it was fine. But it was still a bit scary to see large groups of people being let back into Bulgaria because they didn't have the "right" visas or passports.<br><br>So... what was the most harrowing border crossing you experienced while traveling?