1. to take something over by force
2. A physical act on a smaller, or younger, individual by larger individual in which the victim is hoisted against his or her will to a less advantageous position for the smaller position. Can also be applied to non-physical situations, see below.
3. A usually difficult and laborious act by the little guy, or the under dog, to gain a higher status. Can be applied to numerous situations, such as socioeconomic and social status.
2. Damn, I was just getting my thighs all nice and strong-like, and this meat head came up and big boyed me. Now that gym bunny will think Im a shmuck for sure.
3. I finally big boyed my boss into giving me a raise.
It can also be used by itself to express approval and/or enthusiasm (typically in a high-pitched drawn out fashion).
"That was some BIGBOY shit."
"My stomach hurts" ... "You should take a BIGBOY dump."
"y0, i jus picked up some danky dank kush." Reply in high pitch: "Bigboooooyyyyyyy"