since i remember being alive that whenever i sing or also speak with
funny accent, i tend to start dropping tears, sometimes intenselly. i
feel nothing emotional, or if i do it's a coincidence, it's just runny
eyes. not runny nose. runny eyes. but it gets so intense sometimes i
start sniffing and nose starts running too. but, this doesn't happen
for example when i'm at a karaoke. somehow the mechanism is inhibited.
i've always wanted to know what this is all about, why it happens,
how, and how to inhibit it OR provoke it if i want to... :)

Interesting. I wonder if you feel sad when you drop tears.
This http://www.abc.net.au/catalyst/stories/s1139554.htm item tells
how many people who pull their mouth to one side start to feel sad.
Perhaps when you speak with a funny accent you also make a face or
simply access the left side of your brain. (?)

I have exactly the same thing my whole life and was wondering about it
and find this while googling.

As he said, you don't feel sad it because it's not emotional. It's
just tears. I especially when I am improvising nonsense (like singing
in an invented melody for joking or doing some voice talking crap). So
not when I feel sad at all, but tears come out of my eyes. I've always
wondered what this is.