Asymmetrical warfare isn't a secret known only by the Iraqis or the Afghans. Ukrainians will find their own best ways to frustrate Putin's conquest. You may find his cruelty amusing and that you're a cute fellow for wanting him to crush a peaceful and independent neighbor. Russia tried cruelty and mass genocide against the Afghans and wasn't successful. They've terrorized almost all of their neighbors in the last 200 years. Katyn Massacre ring a bell? The invasion of Poland in 1939? The Holodomor in Ukraine ring a bell? The many different ethnic cleansings ring a bell? Does the Gulag ring a bell?
The Russians won't succeed in Ukraine unless everyone else acts and thinks like you, and they don't.