Blocking
If you don't want to be in contact with someone, you can block them.
Blocking immediately ends the friendship between you and cuts the connection in both directions: the blocked user can't send you a friend request, and you can't send one to them. You also don't find each other in user search, so you drop out of each other's friend lists and search results.
Blocking and unblocking
You can block wherever the user's name appears: in your friend list, among search results, among your team members or the members of a team you searched. Long-press their name and choose Block from the menu that pops up. You find the list of blocked users under Settings → Account → Blocked users, and you can lift the block from there at any time.
The other person doesn't get a notification about the block.
Blocking is a personal decision, not a moderation step. If someone violates the rules, also flag it with the report feature, because blocking alone doesn't reach us.