What you need to buy, Postal 2. This is the best video I've seen on Postal 2 and why it's a great video game.
https://www.youtube.com/watch?v=8yogSHwZPWsYou can also check out Postal 1, which hasn't aged very well mechanically but it's pretty unique in how disturbing a mid-90s PC Game could be.
What you should avoid at all costs in Postal 3, which thematically tries to copy the absurd trashiness of Postal 2 but fails in most aspects. It's buggy, it's not as amusing to play, and it's dev team is invading Ukraine as we speak so they have no plans of releasing the code stopping any chance of the community fixing and improving it.