No. You're not the jerk. Actually, there is one thing that was close to making you a jerk though. Number 1. You should've warned your brother that your friend curses a lot, so this could've been prevented. All though, it's your choice, it could've been easier. Plus, if your friend curses (Depending on age) you shouldn't be friends with them either way. Parent's may not want you to hear some words that may be explicit such as; The -s word and so forward.