This afternoon I passed by a group of high school kids from China going down the street outside of Williams Hall, the office building in which I work. One of the girls said merrily, "Bur'ao", by which she meant Modern Standard Mandarin (MSM) bù zhīdào 不知道 ("[I] don't know").
The retroflex final -r is well known for northern varieties of Mandarin, but in Pekingese it seems that the mighty R has the ability to swallow up whole syllables, as in the example quoted in the previous paragraph.
Here are a couple more instances:
"O gao'r ni" for MSM wǒ gàosu nǐ 我告诉你 ("I tell you")
"Mbr'ao" for MSM wǒmen bù zhīdào 我们不知道 ("We don't know")
I suppose that we might call all of these allegro forms, i.e., changes in phrases induced by increased speed in speaking. Of course, not all such allegro forms involve R:
"Tianmen" for MSM Tiān'ānmén 天安门 ("Gate of Heavenly Peace")
"Dashlar" for MSM Dà Zhàlán 大柵欄 ("Big Paling[s] / Railing[s] / Bars", name of a street in Beijing)
Confronted with some of the more highly elided and distorted forms, all I can do is mutter, "OMG!" and ask "How do they understand each other?"
As if the allegro forms themselves had not boggled my poor mind enough, Jeremy Goldkorn informed me that "OMG" itself has become a popular Internet expression in China:
ǒumàigā 偶麦嘎 (lit. "image / idol / by chance — wheat — creak / squeak / snap") 63,200 ghits
ōmàigā 噢麦嘎 (lit. "oh — wheat — creak / squeak / snap") 368,000 ghits
ǒumǎigā 偶买嘎 (lit. "image / idol / by chance — buy — creak / squeak / snap") 1,510.000 ghits
OMG have mercy upon me!
[Thanks to South Coblin, Cyndy Ning, Liwei Jiao, Jiajia Wang, Gene Buckley, Stephen Dodson, and Julie Wei]