why do my testicles smell like fish

A fishy smell is usually a sign of a yeast infection, although that's almost unheard of in circumcised penises. One possibility where it might be living though is between your scrotum and penis, where your penis rests against the scrotum.

That is a warm, sweaty spot where there is skin to skin contact, perfect for bacteria or yeast growth, and thus odor.

Try an anti-fungal or anti-yeast ointment on that area, and be sure to clean the area well everyday in the shower. Also, if you're wearing briefs now, try switching to boxers for better airflow and less sweat there.
This really bugs me.

If you visit someone else, I think the least these people could do is go before you visit.

There have been occasions when these visitors abuse my hospitality, one actually breaking the wc panel, others pissing on the seat and a few who just didn t pull the chain.

Not pulling the chain is the epitome of laziness. There is nothing more disgusting than seeing an alien giant tu.