The best choice in this scenario would be to Confront the co-worker and point out that it is time for your lunch break and not his. This might be detrimental to social relations, but friendship is not a priority in a professional environment. One must stand up for their rights and avoid being taken advantage of from abusive co-workers, otherwise the co-worker would keep on assuming they can get away with their caprices on expense of oneself in the future.
The worst choice would be to Take your lunch break when you can. This action goes against the principle stated in the previous paragraph. The time for one's own lunch break could be undefined when other co-workers keep taking their free time whenever they like. This abusive behavior can only be resolved with direct confrontation, but avoid using inappropiate communication or violence while doing it - otherwise the situation may result in trouble with the company's administration.
