Rails 3.1 deep nesting with RABL
I got this answer from @calvin-l. The trick was to just map the a.comments then grab the data from each comment that way:
node :annotations do @image.annotations.map { |a| { :id => a.id, :x1 => a.x1, :x2 => a.x2, :y1 => a.y1, :y2 => a.y2, :comments => a.comments.map { |c| { :body => c.body, :created_at => c.created_at, :user => { :id => c.user.id, :facebook_id => c.user.facebook_id, :name => c.user.name, :username => c.user.username } }} }}end