Yeah, I blew one with a big law firm. I was interviewing mostly with DC firms and a few NYC firms for a summer position, but decided to take a flyer on a firm out of Columbus, OH with which one of my section student mentors had done a summer gig and accepted a permanent offer. He was cool and said it was a totally laid back place that I wouldn't be able to find in DC or NYC.
I had the last interview slot on a Thursday afternoon at 4:30. I went to a pretty cool school where the Student Bar Association had free kegs for happy hour in the quad every Thursday at 4. I figured that the interviewer had a long day and being from a cool firm would enjoy a cold one at the end of the day, so I stopped by and picked up a couple beers on the way to the interview. I walked in the room with the beers and explained to him about happy hour Thursdays. The look I got let me know that, instead of being laid back and the interview just being a couple of guys kicking back over some brews, he had a stick up his ass and was appalled. He went through the motions with a lot of tension. I decided, oh well, and enjoyed my beer while casually answering and asking questions.
After our half hour was up, he gave a handshake and a half-hearted "nice to meet you". As he was walking out, I said "hey, do you want to take your beer?", which he had not touched. He said a quick "no thanks" put his head down and headed for his rental car as fast as he could.
Somehow, I didn't receive an offer. I was talking with one of my section mates the next year who had taken an offer and worked there for the summer. I said, oh, I interviewed there and told her about the interview. She said "OH, that was YOU!?" Apparently, word got around the firm about what is inappropriate in a big firm interview. I ended up going with a DC firm where during one of our summer outings, the good ole boy partner in charge of my group wound up buying rounds of shots of Wild Turkey until he drank me under the table.