I'm not sure if I completely agree with this because you can be happy from being with other people, but I think I would agree more if this said positivity instead. Being happy is a very personal thing and it really has nothing to do with anyone else.
He smiled, sitting back in his armchair, carefully setting the bookmark in its place before placing the book on the ground. "Go on then," He muttered, watching the security footage on his tablet. "Underestimate me." (RP anyone?