Use a, b, c, e and d to represent five people:
AB, AC, AD, AE: Strong and active handshake (A)
BC, BD, BE: Tao Tao takes the initiative to shake hands (B)
CD, CE: Lili shakes hands actively (c)
De: Niu Niu shakes hands actively (D)
Beibei did not take the initiative to shake hands, but passively shook hands with four other people:
That is, shake hands with Zhuang Zhuang, Tao Tao, Lili and Niu Niu once each, ***4 times.