You could actually say almost anything. I will reward you with an amount of mana that reflects my impressed-ness. examples:

@firstuserhere : "I walked 100k steps in a day once!"

me, probably: 5000 mana (note, i'm not actually going to give you 5000 mana)

@ithildulin : "I learned Paganini 15!"

me, probably: 5 bILLION mana!

By anything, i mean anything. You can tell me an impressive feat of yours, a talent (athletic, musical, etc.), a pet, an experience (vacation, concert, etc.), or anything else. Silly things are also appreciated. JOKES, i forgot about jokes. If its an especially good joke, then you are happy and I am happy.

If you would also like to be hugely impressed by the great community which is Manifold, feel free to add to the bounty.