1. 加油 - This phrase (pronounced jia-you), which literally translates to "accelerate", means "Work hard/go get-em!" in Chinese slang. Typically you say this to friends and/or co-workers when they are about to undertake some task OR if they have been working very hard at a task. The Japanese equivalent of this is roughly (頑張って!)
When your buddy is about to take an exam, or when your wife is about to interview for a new job, or if your dad has been working in the shop for over 10 hours ... you would say "加油!" to them in each case.
2. 哇噻 (wa-sai, no literal meaning) this is an expression of surprise in Asia.. In the US we have "WOW", Japan has "iiiiiye", Taiwan/China has "wa-sai".
If you hear that your friend has run down the street naked in Taipei to catch the bus to visit his mom, the proper reply would be "哇噻!“
3. 十三點 (shi san dian - translates to 13 o'clock) OR 三八 (san-ba translates to 3-8). Both these phrases are used on women that are snobby and/or bitchy. While both are used, the latter 3-8 is more common in Taiwan.
Initially, I had a difficult time trying to come up with an example of this until I watched an episode of "The Simple Life" ... if you want examples of people that are 3-8... just think Nicole and Paris ... “他們好三八!” (ta-men hao-san-ba, they are really 3-8)
ALSO BE CAREFUL about using these expressions with Chinese women... (from what I've been told) they are pretty offensive and most likely will get you slapped and/or punched by their men