"Heck yeah I'm metagaming, but I don't care for something like this"
?!?!?!?
No, that's not enough emphasis.
?!?!?!?!?!?!?!?!?!?!?
If a PC pulled a stunt like this just to grab attention for himself and then he had the temerity to tell me that he didn't care for me as DM doing my job, I'd tell him fine, go find a DM that lets you metagame to your hearts content - I'm here to arbitrate a roleplaying game not facilitate your personal ego trip. If you want to metagame and get in contests with me, then I don't have time to waste on you so get off my table, because there is a game going on and you are getting in the way.
"You think only geniouses invent things?"
No, of course not. If I thought _only_ geniouses invented things I would have made the DC significantly higher than 20 to rule ordinary people out of the equation. I think alot of things are invented by accident, or by mistake, or by dumb luck, but it certainly helps to be a genious. I think most things are invented by creative, intelligent, thoughtful, knowledgable people. I think very little of the RP skills of a player with a 6 intelligence character (or even an average int character) who thinks he should be allowed to go around inventing things just because his player can describe how they are done. It took 70,000 years of people plenty smarter than you before anyone thought to invent something obvious like _hay_, so don't try to tell me that you should be allowed to go around inventing everything invented in the last 1000 years just because they seem obvious to the player.
Look, as far as a character inventing sandwiches goes, I find it slightly amusing and creative enough to somewhat excuse the metagaming. But its still metagaming, not roleplaying and I'm not going to let you set precedents which I then have to overrule by DM fiat. I have a responcibility to all of my players to be fair and impartial. If you decide, "Heck, I'm going to invent a sandwich even though I know it is metagaming", and I say, "Ok, no harm in that.", then what happens when Joe Gamer wants to invent blue jeans, simple compound interest, algebra, the assembly line, the bicycle, or the telescope? What am I so supposed to say, "Heh, I let Tysr invent sandwiches, but inventing sweetened condenced milk is just out of the question." Why? The two things aren't really all that different. Am I just supposed to let anyone invent anything he can describe the steps to in detail? What kind of DM's rule is "I'll let you invent things if I think it is harmless, but if it is going to radically alter the culture of my world THEN I'll crack down on your metagaming." That's called 'railroading'. DM's don't decide what players do. They decide what players can do.
You want to jump over the chasm, fine, make a DC 35 jump check. You want to convince the gaurd to let you in the gate after nightfall, fine, tell me what your story is and make a DC 25 bluff or diplomacy check. You want to invent something that doesn't exist, fine, make an idea roll and a profession or craft check. If you don't like my rulings, fine, no one is making you play.