the accident at tokyo university's cafeteria

Last week, I found the nuance between “should” and “have to”

As I work at Tokyo University’s cafeteria, some men(1of them seemed cannot use Japanese) were coming and dropped beer bottle into the sink. For sure, it is not the place return the bottle. So I decided to warn them to return the bottle to right place.
And I said to a man who seemed not use Japanese” You should return the bottle over there”　in English but he didn’t catch and said “sorry?”　roughly.
I said that calmer again. Although I warned calmer and clearly to him, he got angry more and more, eventually he argued to me. I couldn’t understand and got confused a little bit. Then, one of his friend taught me “should means too strong in this situation.”
I assume that but a man who got angry with me was still angry even he tried to hit me but he was stopped by his friends after all.

I learned the nuance between “should” and “have to” or another polite phrase at that time. Next time, I’d say “please could you return the bottle over there.”