There’s a huge divide between casual spoken and academic language when written and a slightly smaller gap when spoken. The problem for international speakers who arrive at Masters or higher levels is to know what is acceptable and what is not. Most have great spoken skills when in the pub/café. Many do not understand some words just do not get used in formal and semi-formal environments – or even in domestic ones. We are not all Prince Philip! (http://www.independent.co.uk/news/uk/prince-philip-impatient-at-photographer-just-take-the-fing-picture–video-10381185.html)
Those of us with less regal connections have to manage with a much broader, more detailed vocabulary. That’s not a bad deal if you really want to be rude. A wider choice of vocabulary can be really offensive as it is thought-through rather than a casual use of ‘rude’ words that have become nothing more than casual adjectives used by the literally inept. If you are a non-native-speaker, however, the safest route is to avoid the words you were taught in the pub, and even in emails and conversations, and stick to words you will find in a large, old-fashioned, school-level dictionary. Swearing in an academic thesis is just wrong – unless that is the subject of the thesis. At a social level, international academics have a really hard time of it working out what is acceptable and what is not. If in doubt, I’d stick to the school-level dictionary. Getting swearing wrong is easy. Talking in a way that does not embarrass people soley because of the vocabulary is easy – just pick a large school dictionary and add in any necessary subject vocabulary.