Spitting can be an unwanted urge as a result of a tic-disorder. It can be regarded as anti-social behaviour, even though the urge is involuntary. Spitting in public can be problematic, especially if directed at someone.
Tourettes Action in the UK defines spitting tics as a complex tic in their FAQ section.
Spitting- if a tic- comes from the same processes as any other tic, and needs to be treated in the same way.
Spitting in someones direction can be misinterpreted as an aggressive or hateful act. With tics, this is not the case.
A combination of Tourette and OCD
Spitting may feel more like a compulsion in OCD. If there is a worry of contamination or poisoning for example, there may be an urge to spit to relieve anxiety.
Tourettic-OCD may better explain some experiences individuals have, with an overlap of tics and intrusive thoughts.