Yes, it's a concert. I do it all of the time and feel that people who get angry at me are unjust.
Yes, I think it's OK, but I don't do it.
No, I don't think it's OK, but it doesn't necessarily offend me and I don't get mad at the people who do it.
No, it's not OK. I do express my displeasures with people that try to push their way through the crowd.