If you want to gain height, you need to pick someone up by the lower half of their body, but any lower than their waist and they risk losing their balance if they tip forward. Their waist accordingly goes up to your shoulder height, so you're not really getting anything but their back close to your face.

It is intended to be more mischief than anything sexual. Toshi's idea of flirting isn't really about hooking up, it's just the type of personality he thinks is cool.