Convention Etiquette

I've been to a lot cons and have always tried my best to be polite and nice. I was just wondering what you guys think about what you should and should not do at a con or event ? EX: Don't just run up and hug someone (Someones ripped a piece off my cosplay doing this I was very upset)

Don't criticize the cosplayers like two ft away from them. At the cons I have been to there have been alot of perfectionist assholes who would always find something wrong with peoples costumes and talk loudly what they should have done better to their groups. I admire anyone bold enough to put the money and time into cosplaying. Cosplayers= awesome!