Actually, if it was a true acoustic set, there wouldn't be a mic cord to yank out. Acoustic means no amplified sound at all, just the natural voice and instruments. You might be thinking of a regular live set with a PA system. I've seen people mix that up before. The cable fail is still funny, though! Just a different kind of show.
Wait, that's not always the case though. I've been to plenty of shows called acoustic where they use a mic for the singer so the crowd can hear. Like at a small club, the guitar was natural but the vocal had a thin cable running to a little amp. They still call it acoustic because the instruments aren't plugged in. So a cord getting yanked could totally happen.
Hah, classic cable fail! I totally did that at a buddy's open mic night, tripped on the extension cord and killed the power. The whole place went silent for a second before everyone cracked up.