In 1963 China signed an agreement with Pakistan formally receiving a part of Kashmir which Pakistan didn't even control (it was controlled by India). In 1967 China invaded India during the Chola incident. In 1969 China invaded the USSR in the Daman island war which caused (or crowned?) the Sino-Soviet split. And all the resultant territorial disputes would not get settled for decades (if at all).
What made Mao act like that?
It wasn't necessarily "Mao" that was responsible for these actions. If anything, Zhou Enlai played a bigger part, having been China's foreign minister up until the 1960s.
Before we get to the Chola incident and the 1963 Sino-Pakistan agreement, you should understand that the Chola incident was a result of the Sino-Indian War of 1962. This was due to a border conflict between China and India. India was concerned about seeming weak due to territorial conflicts with Pakistan, while China was concerned that India was allying with the Soviets to surround China, as well as subverting Chinese rule in recently annexed Tibet. Indian Prime Minister Nehru instituted the Forward Policy, which authorized Indian troops to move into disputed regions held by Chinese troops. As they moved deeper into these regions, they came into conflict with PRC troops, eventually resulting in several firefights. The Chinese were incensed as they believed this was part of a plan to destabilize Tibet, so they elected to attack India to punish them. The resulting treaty resulted in a peace that more or less demarcates the current borders, although there were still border disputes for years after the war. As a result of this incident, China courted Pakistan as an ally against India, to help offset the Soviet Union's courting of India.
On a similar note, the Sino-Soviet split had already been in motion for a long time. China had significant territorial claims on Russia, who had signed one of the "unequal treaties" in the 1800s to claim Outer Manchuria, or Primorye, as well as the annexation of the area known as Tannu Tava in the West, as well as border incidents in Mongolia and Xinjiang. As a result, to satisfy Chinese revanchism, China attempted to negotiate with the Soviet Union to "revise" these treaties which the Soviet Union found to be unacceptable. As a result, Chinese troops attacked Russian forces in a series of border skirmishes over the island and various other territories.
Sources:
Maxwell, India's China War
Luthi, the Sino-Soviet Split