Funny enough I've just done something similar today. I had something stuck to my front tyre and I was worried that I would get a puncture so I reached down with my finger to flick it off. I only clipped the tyre and realised that it might take my finger end off so I made a fist and used the gloved knuckle to knock the foreign object off. It worked and I carried on oblivious but might exact a bit more caution in the future after hearing this story.