Doubtless, if you're a pokemon fan you've seen this one coming. Pikablu!
According to the myth, talking to Oak in R/B/Y a hundred or thousand times (depending on the schoolyard you heard the rumor in) will yield you a Pikablu/Pikatwo/Pikayou/Pikawho/Pikashoe/Pikaglue/Pikapoo/Pikamew/Pikaclue/Pikagoo/Pikaloo/Pikaboo/Pikamoo/slap in the face/whatever(quote http://glitchcity.info/docs/myths). I actually believed this once.
Why it Doesn't Work? Edit
Simple: There's no such thing. Pikablu/Pikatwo/Pikayou/Pikawho/Pikashoe/Pikaglue/Pikapoo/Pikamew/Pikaclue/Pikagoo/Pikaloo/Pikaboo/Pikamoo/pokemon. Zilch, zip. The only secret pokemon in R/B/Y is Mew. (see Mew Glitch)You can still try. Oak might be in a good mood and give you a slap in the face.
http://glitchcity.info/docs/myths: some glitch myths here