gistfile1.txt

user.rb
def unfollow!(other_user)
  friendships.find_by_followed_id(other_user.id).destroy
end

users/show.html.erb
<% unless @user == current_user %>
  <% if current_user.friends_with?(@user) %>
    <%= form_for current_user.friendships.find_by_followed_id(@user),
                 html: { method: :delete } do |f| %>
      <%= f.submit "Unfollow" %>
    <% end %>
  <% else %>
    <%= link_to "Follow", friendships_path(:friend_id => @user), :method => :post, class: "btn-sml btn-accent" %>
  <% end %>
<% end %>