def show
  @user = User.find(params[:id])
  @users = User.all
  @friends = @user.friends
end

<tr>
  <td>
    <%= gravatar_for user, size: 30 %>
  </td>
  <td>
    <%= user.name %>
  </td>
  <td>
    <% if current_user.friends.exists?(user) %>
        <%= link_to 'Remove friend', friendship, :method => :delete %>
    <% else %>
        <%= link_to 'Add friend', friendships_path(:friend_id => user), method: :post %>
    <% end %>
  </td>
</tr>

<%= link_to 'Remove friend', user, :method => :delete %>

<%= link_to 'Remove friend', friendship_path(user), :method => :delete %>

<%= link_to 'Remove friend', @user, :method => :delete %>