I'd probably see her and just collapse, wake up in hospital and cry because i relise i just fainted in front of Lady GaGa and didn't get chance to tell how how much i adore her.
"OMG IT'S LADY GAGA!! Hi!! I'm a BIG Fan of your work! Although your Musik Videos kinda scare me...wait, did I just say that?!? I meant NO!! Wait, what am I saying? Yes, they do scare me, but I still Liebe Du anyway!!!! Du HAVE A WONDERFUL VOICE, GAGA!" and then, thus finally humiliating myself to the extreme, I would take a quick picture of her, then run away.....