You can use ! and %in%:
filtered_users <- filter(users, !user_id %in% c(1, 5, 6, 7, 11, 17, 18))
This is based on https://stackoverflow.com/a/34444336/1152809. I just googled "dplyr not in" and this was the first result. Google is your friend when learning new things. Also, as @thelatemail said, %in% is a base R function.
