Chemistry jokes are deadly when you don't understand the notation! H 2 O is water, but H 2 O 2 is hydrogen peroxide - a powerful oxidizer that'll bleach your hair, disinfect wounds, and apparently end your bar crawl permanently. The second guy thought he was ordering the same drink but accidentally requested a chemical that would absolutely destroy his insides. Talk about a fatal misunderstanding of subscripts! Next time, just order a beer like a normal person instead of trying to sound smart with your chemistry knowledge.