"If cows are made of lemons..." means that by being a lemon I am a cow, and will digest and create you, you cowpat.
On another, copied and pasted, note...
"So these tourists are on holiday in Greece, wandering around, and they hire this guy at a bar to take them on a tour. So they're walking around the island they are staying on, and the guy is pointing stuff out to the two tourists. As they near the port, the guide points to a small fleet of boats docked there.
"You see those ships? I built them, by myself! And do they call me Lekas the ship builder? NO!"
the tour continues, and eventually they see a large olive grove. The guide points at the trees and scornfully addresses the tourists.
"You see those olive trees? I planted that whole grove myself! And do they call me Lekas the olive grower? NO!"
The tourists continue on, somewhat confused by the guide's anger but enjoying the tour nontheless.
As they walk down a road, they pass a row of houses, and the guide waves his hands expansively.
"You see those houses? I built them all, by hand, by myself! And do they call me Lekas the house builder? NO! But I have sex with one dog, one...dog...""