Please don't. It's really obnoxious when people try to sneak in front of you when you have paid for your specific seat. I always tell security if someone steps in front of me and is standing where they aren't supposed to and it's in my line of sight. I paid for my seat, I deserve to be that many rows away from the stage. People who try to sneak into someone else's seat put a damper on the experience for the people around them.

If it's general admission, it's still obnoxious when someone squeezes in front of you, but it's not like they are standing in someone else's specific spot. Just stay in your seat. If you are too short for floor seats, opt for the lower level. Don't be an ass.