Chuck somebody under the chin
Definition 1 of 1
Pro Tip 1/3Affectionate Gesture
Used to show care or fondness, often between parents and children or close friends. 
She affectionately chucked her daughter under the chin after the performance.
Pro Tip 2/3Not for Strangers
Inappropriate with those you're not close to; it may be seen as too personal or invasive. 
Don't chuck someone under the chin if you're not familiar with them; it's not always welcome.
Pro Tip 3/3Positive Reinforcement
It's often used to encourage or compliment someone, especially children. 
After acing the test, his mother gave him a joyful chuck under the chin.