Good afternoon and welcome to todays class in Finnish.
"Ei!" is no, but is also like "Oi!", an exclamation to say "stop it", get attention and/or warn people off. The reasons finns don't say "Oi!" is probably because "OY" in Finnish means "incorporated". Well, that and the fact that finns don't speak English they speak Finnish. Ei käy! is "no way!" and Ei ikinä! is "Never!". This surreal little clip from the Oulu Police Force aired on YLE, shows how to prevent a rape or attack when you have no weapons. Just use the force that all Finnish women are equipped with, a.k.a the word NO! If "Ei!" and a shove doesn't help, you may also smack your attacker over the head with your purse. P.S. always carry bricks in your purse.
Yes, I find the entire clip laughable, but we have similar things on tax funded Swedish public broadcasting, including ad campaigns that mock the idea of ad campaigns, so I'm used to it.