From this angle you've managed to secure a perfect view of the stage. You're not at the front, but luckily the geometry of the floor angle and height differentials is working in your favor. Just as you're congratulating yourself on scoring such an ideal spot, along comes what must be an NBA center, judging by his height. He towers over the crowd as he makes his way toward you. You silently, or maybe not so silently, pray that he'll lumber past, but he spots the open vista and parks himself there. The opening band finishes up, and the main act comes out. You know this by the roar of the crowd alone because the entire stage has been removed from your view by the behemoth in front of you. All you see is T-shirt.
Have a heart, Yao Ming! Be aware of your stature and do what you can to limit the damage.
But the empathy must be mutual. It's not tall guy's fault that he's a walking house. So don't berate him or shoot dirty looks — just politely ask him to shift over if possible. Better yet, if your dimensions run petite, consider bringing something to stand on. Something collapsible though — see the previous commandment re: luggage.