This thread is hilarious and very interesting. I would like to share a couple of things too.
1. Some of my friends always pronounced 's' before the 'k' in every word when it is supposed to be the other way around. e.g. Riksha (rishka), vicks (vishk) and some do it the other way like desk (deks) and disk (dicks) like someone mentioned above.

2. I had a friend who pronounced "e" in the word "pet" long and it sounded like "I like to keep a पेट . 

3. About mistaking one word for another like the awful/awesome example above. A friend of mine who happens to be a doctor had a peson say to him," डाक्टर साहब, मेरो श्रीमतीलाई pregnant बनाइ दिनुपर्‍यो। (he meant to say delivery). 

4. i have a distant niece who happens to be half white and one day she said to her dad and me, "You guys cannot pronounce "s" by itself." I told her it's a South Asian thing and had to show her the "ispider man" song on youtube for verification.Luckily, I happen to have adapted to the hissing sound in school, style, sprite, schedule etc.

5. about "shanti" and "santi", here's what I have to say. The Nepali language itself does not contain any श and ष. We only have paatalo "sa" in Nepali and all the words that contain श and ष are तत्सम words from Sanskrit. eg. If you say ten in Sanskrit, it is दशम् but when you convert it in Nepali it is दस and not दश. These are called  तद्भव words. A pure Nepali word will only have "paatalo sa" e.g. कोसिस and not कोशिश. But having said that, I believe that, we Nepalese should try to pronounce "Sh" and "S" correctly when we are speaking Hindi and "Shanti" being a "tansam" should be pronounced with a "Sh". Thats the whole reason of having श and ष in Nepali "Varnamala".

6. There is a difference between how Nepalese and Indians pronounce and write some words. I don't think we Nepalis are necessarily wrong in every case although there are few places where we seem to require some adaptation. 
e.g. When asked to write "fax" in our language to an Indian friend and me at work, here's how each of us wrote it.