I speak Mandarin with my wife sometimes out of China, like in the Philippines or at home in Canada. 

Since most people don't understand we can discuss things or I can explain things to her in Chinese so she isn't embarrassed. In China, English is like our secret language... because most people can't really understand when not around foreigners.

And outside China it turns to Chinese.  

  Does saying "Two spling lolls an' a numba flee" count? (Oh God, that's so lame).

Only when I yell "NIHAOOOOOOOOOOOOOOOOOOOOOOO" at Chinese looking people in shopping malls. 

Ai-ya? Sometimes I use that when I go back home. Not often tho. There aren't a lot of Chinese in my hometown.

Speaking Chinese with Chinese people is challenging.

Not every time just in rare cases otherwise speaks British English.

only 2 words
" ni hao "  and " xie xie "
 

A new account doing the same job, might as well not change accounts. 

Too often. "You're the foreigner, small-eyes"

Never used it back in the UK but I did one time in Bali...

Was sat outside a nice coffee shop in Ubud, espresso on table, enjoying watching the world go by while having a smoke. Chinese couple, 30-something order drinks...like a lot of us do here by pointing at the menu. Next thing there’s a bit of polite confusion...lady is asking for something in Chinese, Balinese staff have no idea. I’m a bit of a nosey sod so look over...

“Bu yao bing kuai” says the lady, “what?” replies the barista...so being a helpful soul walked over and asked “ni bu yao bing kuai ma?”  I get an amazed look and a “shi de” back. Tell barista she doesn’t want ice & go back to my seat. Next thing I’m getting thanked and told my Chinese is “li hai”! Had brief conversation with them and they went away smiling. 

Nice to be helpful sometimes...