class Like < ActiveRecord::Base

   belongs_to :likeable, :polymorphic => true
   belongs_to :profile

end

class Comment < ActiveRecord::Base
  #existing associations
  belongs_to :commentable, :polymorphic => true
  belongs_to :profile

  # need to associate through likeable_id/likeable_type
end

class Profile < ActiveRecord::Base
  #...
  has_many :likes

  #need to associate to liked_comments

end