Steven Pinker, a psycholinguist explores the connection between language and psychology and we will examine his research to explain the social reason behind your swearing, and the root of the offence of the swear word you used! His research has found that one commonality across languages is that bodily fluids are used as swear words.
Before we get into the whys and whats of shit, piss and “bloody hell!” Let’s look at what swearing does to the brain. Pinker notes that taboo words such as swear words are thought to be processed involuntarily. He states, "You can't read a taboo word without the negative emotion that clings to it." In the brain, it is the right hemisphere that lights up in response to swear words, and more specifically they cause reactions in the basal ganglia and amygdala. Both of these are buried deep in the brain. The basal ganglia are a group of structures responsible for the production and inhibition of behaviours, and the amygdala processes the perception of the offending work. It is the area of the brain that is activated in response to threats.
Stating that bodily fluids are vectors of disease, Pinker points towards the evolutionary explanation of why humans have adapted to be disgusted by bodily effluvia. It is interesting that this disgust manifests in our linguistic system and helps to both influence cultural disgust and be influenced by cultural disgust.
Pinker found other categories of swear words that help demonstrate the impact of culture on swearing, including religious words. In highly religious societies, words such as Jesus Christ are used as swear words and as societies become more secular, such words become less offensive. Bodily fluids, however, seem to remain offensive across cultures. How much of this is informed by Pinker's evolutionary explanation, and how much of it deals with culturally created disgust?
Pinker answers what swearing does in a social setting. Thinking back to that last time you swore, do you know why you wanted to press on those negative emotions in others, and yourself? According to Pinker, it is one of a few reasons, perhaps you wanted to offend, for example, "so I've been looking after the children while you've been fucking my best friend?" Not familiar? That's probably a good thing. Maybe you used it to assert your 'coolness', to rouse a listener's attention, or to express informality amongst a group.
Still no? Well, maybe it was cathartic. Did you spill coffee on your shirt and shout "fuck" really loudly? Or scream "pissing-shit-balls" as you fell down the stairs? Unlike the previous examples, this "pissing-shit-balls I'm falling down the stairs" type of swearing doesn't seem to serve an immediate social function. Instead, Pinker explains that when mammals are trapped, shocked or perceive danger, we have adapted to let out a howl, presumably designed to intimidate a potential attacker. Because humans have a linguistic system, our evolutionary intimidation technique often manifests as an outburst of swear words. 
So, now you can analyse your last swear word to the nth degree, and the last swear word your office mate exclaimed and your next swear word, and the one after that! You are welcome!