O! - EASY
enter the gas station and you'll see a monster that keeps saying "O" once the conversation is over you will get the achievement

Not this time - MEDIUM
be mean to the girl and once she says "looks like "(name)" doesn't help me at all..." you will get the achievement

Milk bought - HARD
be nice and when you save the girl form the truck pick "its a cruel world out there" then pick the "..." and for the answers where you need to type say "Yes" (capitalization is needed) and after that say maybe and shortly you will reach home and get the achievement