You will never exaggerate when you speak good things of God. It is not possible to do so. Try, dear brethren, and boast in the Lord. (Charles Spurgeon)
What do you exaggerate about the most frequently? Is it your weight, age, or even your income? Is it the state or condition of your soul, telling someone you are "fine" instead of being truthful about the fact life is falling apart all around you? Is it perhaps the small things like that you'd be happy to do something for someone, all the while begrudging that they are asking for yet another favor from you? It seems we have become a society that appreciates being in-genuine instead of remaining true to our integrity. We boast about stuff we really don't control, while we remain silent about stuff we probably need to be more forthcoming with. It is far better to boast in what is true, reliable, and consistent - the grace and love of God!
As Paul indicates, the cross is the center of our "boasting" - for nothing compares to the ability and power of the cross. There is no life-change apart from grace, although we might try our best to change things up a bit. We are still the same at the core of our being until the cross is embraced and Christ becomes our focus! The cross changes our interests - it redirects our attention to the things that really should warrant our attention. The condition of our soul is what is changed with the cross - our spirit united with his, our souls begin to be transformed from self-seeking, self-preserving, and self-boasting actions and attitudes.
Our interest in the things we once felt a great pull toward often begins to wane as we grow closer to Jesus in our "heart affection and attention". If you want to be able to explain salvation to someone who is unchurched, perhaps that is the clearest evidence they will ever need - to know that salvation doesn't "restrict" you, but it "refocuses" you. If you speak with an unbeliever, they will often focus on what it is you "cannot do" as a Christian and the stuff you "have to do" such as going to church and reading your Bible. They don't "get" that you do those things not so much because you "have to", but because your interests change as grace enters into you. You also probably take some "heat" about the things you need to "give up" - cursing, gossip, and even going to the bar or somewhere you used to frequent.
What the unbeliever doesn't understand is that you aren't "giving up" anything - your interests in those things have changed and you no longer desire to pursue them. You aren't being made to "give up" anything - it is as though you just know it is time to move away from those things and move toward something else. It isn't a burden - it is a joy. I think this is the most misunderstood thing about "being a Christian" - the fact that life-change is occurring and your interests are changing right along with that change! Our interest in the worldly things we once felt drawn toward isn't the same anymore. Little by little, this transformation is taking place - and our lives reveal evidence of grace's pull being stronger than the world's!
Boast about the change going on inside, and the one who is at work reordering your interests - this is a good thing to boast about! Just sayin!