Here are some ways to burn bridges:
1. Gossip about people
2. Don't return phone calls
3. Be dishonest
4. Only talk to people when you want something from them
5. Be unreliable
6. Talk big and never follow through
7. Degrade others
8. Be self-centered
9. Treat people bad when their down and out
10. Look down on people who are below you in their career, position, economic status, etc.
11. Be a know it all