It happened only once to me, to which I replied "congrats." :'D It looks cheerful/neutral, but if they could hear the tone of my reply, it would be more sarcastic XD
But I know those types of comments, I saw them a lot on other sites, to which some escalated with people replying which number they are "second!", "Third!" and so on. SOmetimes it's funny, but usually it's just meh.