The term 'social pest' can be defined as someone who is intrusive and annoying in social situations. The crossword solution for this term is ANT, which is a three-letter word. Ants are small insects that live in colonies and are known for their hard work and cooperation. They are also known for being persistent and often considered pests when they invade homes or gardens. In this context, the term 'social pest' can be used to describe someone who is intrusive and annoying in social situations, much like an ANT invading a home or garden.