How can we report users like this https://parenting.stackexchange.com/users/18981/jeff ? (If you want to know why he needs to be removed, just check out his answers.)
These are ways to handle users who aren't behaving appropriately, but they all need at least 5 reputation.
The flag system (15 rep). (In this case, "rude or abusive".)
Downvote (125 rep).
If enough users downvote an answer and flag it as abusive, it becomes hidden (for users who aren't very high rep) and eventually the system will automatically take action even if none of the moderators are currently online.
Chat (20 rep) and meta (5 rep) also work for alerting mods to problems.