ShadowMecc,Quote
ShadowMecc
Quote
yaumingfai
. . .
嗰班人係蠢到不得了嘅。
That group of people is extremely stupid.
This is not even close to an accurate translation. 不得了 does not mean "extremely" or anything similar to that.
不 is the formal equivalent of 唔 (pronounced as "m", used as a negative particle). 得, you should know that it means something along the lines of "able". 了 is used in formal writing and Mandarin, to indicate the finishing of something (e.g., an action).
不得了, together, means "unable", "can't be", "unbearable".
The example of 佢係肥都到不得了 doesn't make any logical or syntax-correct sense. The proper way for the phrasing of that is 佢肥到不得了, which in itself means "He's grown to unbearable fatness", or something of the sort.
不得了 is a very common term and does mean "extremely" and I agree with the definition from yaumingfai and Simon.