To ganesh someone is to place one's arm in between another's arm and torso such that it appears that the person (the ganeshee) has three arms. It can be done by more than one ganeshors to one ganeshee to create the illusion of more arms protruding from the ganeshee. The action is usually performed without the ganeshee's prior knowledge.
The word is believed to be derived from the Hindu god Ganesha whom has many pairs of arms.
"I will ganesh Sam", "I am ganeshing Sam", "I have ganeshed Sam", "Will you ganesh Sam?", etc.