This character is attempting to perform a Boobjob, but their breasts are too small to do it properly. Apply i1628 to the receiving character.
Naizuri literally means "rubbing against nothing".
Note: It's possible that the character realises the futility of their attempt and and helps our with their hands for example by rubbing the penis between their chest and the palms of their hands. The trait still applies in such cases.
NSFW Example 1
NSFW Example 2
rubbing against nothing