You can make a claim for harassment even if the incident took place outside of the workplace at a work-related social event, for example, an office party. The law interprets the workplace in this type of situation in a fairly wide context. If events take place in the course of employment the same rules could apply as in the workplace itself. Witnesses can be helpful as can a note which details the incident as this could become important evidence should you decide to take the claim to the Employment Tribunal.