The medical journal Movement Disorders reported two case studies of people who were deaf from birth and had the tic disorder Tourettes, leading them to compulsively swear in sign language.

Tourettes is often associated with compulsive swearing, although this only happens in a minority of cases. It is more commonly associated with compulsive actions, that can be non-word vocal sounds, or actions that range from eye-blinks to hair-combing like actions.

However, in some people compulsive swearing, known as coprolalia, does appear, and in these two cases studies, it seems this can even be expressed through sign in people who have sign language as their first language.

This is from a 2001 case study:

Here we present a 31-year-old man with prelingual deafness who had motor and vocal tics as well as coprolalia expressed through sign language. He would feel a compulsion to use the sign for ‚Äúcunt‚Äù (see Fig. 1: [top]) in contexts (grammatical and social) that were not appropriate. This is essentially the sign for the medical term ‚Äúvagina‚Äù except that the sign is pushed toward the person at whom it is aimed and accompanied by threatening body language and facial expression. The patient would then feel embarrassed about the compulsion and aim to disguise it as another sign. Commonly, this would be the sign for ‚Äúpetrol pump‚Äù (see Fig. 2: [bottom]). This can also be used to symbolise a small watering can.

There’s also loads of great guides to sign language on the net, including a guide to swearing and a guide to flirting if ever you find yourself wanting to chat up a hot deaf babe or sexy deaf boy.

Link to first case study (vaguely via MeFi).

Link to PubMed entry for same.

Link to second case study (mentioned above).

Link to PubMed entry for same.