steal my thunder!

Apparently, this phrase originated back in the olden times, in Shakespeare's theatre. You see, when they wanted thunder as a sound effect in a play, one of the stage hand types would roll a canon ball (yes - a canon ball) across some metal stuff way up above the stage. Understandably, this was quite a sought after job, and it often happened that one stage hand had their canon ready to roll across the metal when another stage hand would steal the canon ball and take all of the noise-making glory for themselves. Hence the phrase 'stealing one's thunder', meaning stealing the limelight away from someone.