Hollywood's a fickle business, and you gotta learn how to move fast if you wanna dodge the crowds -- so we wanna see if you can guess who this on-the-go star is!

We ran into this actor -- for all of a few seconds -- on the streets of Manhattan a few years back, when he was signing a few autographs for some lucky fans ... but he ended up being pulled away after putting his signature on a handful of photos.

Hey, we're sure his fans had the best time -- well, 20 seconds or so -- when he was around!

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