You may hear it said that doctors sometimes write cryptic abbreviations on certain patients notes, as a warning or hint to other practitioners who may later see them. The practice is on the decline as in many countries, facetious or insulting acronyms are now considered unethical and unacceptable, and patients can demand access to their medical records.
The most well known is probably "NFN", which is supposed to mean "Normal For Norfolk". According to Wikipedia,
The term is considered derogatory because it portrays people from Norfolk as normally being strange, or peculiar with an inference that they are in-bred. The portrayal of people from Norfolk in this light is a common stereotype in England.
Within Norfolk itself, the phrase may also be known as "Normal for Wisbech", which is in neighbouring Cambridgeshire. In addition, most areas of the country have a regional variation of NFN, e.g. in North-West England, NFS (Normal for Stoke) may be heard.
Others include FLK, (funny looking kid - possibly inbred or with genetic quirks), GLM (good looking mum), LOBNH (Lights On But Nobody Home) UBI ("Unexplained Beer Injury) and Oligoneuronal (thick).
I won't explain what "code brown" and "code yellow" emergencies are...