> weekly or monthly basis

So not "extremely common" as the commenter upthread said.

> liquid left on seats

As in, something spilled?

> litter

Lol. Only on a weekly or monthly basis?

> gag-inducing smelly people

I think some people are looking to be judgmental.

> antisocial behavior

That's taking it pretty far; it's easy to ignore these things which are almost always harmless - none have ever affected my life. Maybe being judgmental and (for some) hateful is the real and dangerous antisocial behavior - the consequences have had real and awful consequences for many.