[this_is_not_you]

Top of my head:

* Who are you messaging most (best friends, family). If they like stuff, you might like the same stuff.

* When are you messaging people (awake time > profiling)

* Messaging companies (obvious, what are you into)

[theshrike79]

Also: Where are you messaging

You clicked an ad about Product X, you're messaging your friend B from a store that sells Product X

-> Serve ads about Product X to B.