im a foreigner living here for 5 years. I would be able to share some.
You can pretty much do everything here. Just don't get caught.
chewing gums is okay but make sure you don't stick it under the bus seat or spit it out in crowded places like orchard and city hall. A lot of civillian officers on the look out.
litering your cigarette butt, spiting are basic. You must know this already. Making too much noise on a house party after 10 pm is illegal too. You don't want the police knocking at your doorstep in this case. Unless you live in a landed property
it would be okay I guess.
Drugs ( no way you can score some here )
Rape ( Youre dead )
Murder ( I don't think you want to kill your boss here )
Terrorism ( You don't want to be famous like Mas Salamat )
Shoplifting ( Lots of survaillance cameras everywhere )
Sexual Assault ( even verbally, a woman can charge you and make your life like hell )
Porn ( If you purchase it in Geylang )
And a lot more. I think they should come up with laws against people who don't take a shower. The mrt in the mornings just stinks like F*&.