Sharists are those people who spend their time on Facebook just sharing posts. They are usually single, hence all the free time to bore us with their useless posts.
Ever since they dumped her, she's been a big sharist on Facebook.
420, 4:20, or 4/20 (pronounced four-twenty) is cannabis culture slang for weed consumption, especially smoking around the time 4:20 p.m., and also refers to cannabis-oriented celebrations that take place annually on April 20th.