All of Ponyboy's greaser pals--including his brothers--seem to understand that Pony is not like the rest of them. Pony excels at school: He makes good grades, likes to write, and is a member of the track team. His friends all know that Pony has a chance to make it out of town (presumably Tulsa, Oklahoma), go to college and make something of himself. The other greasers already have given up on ever rising above their economic and social status: Soda has dropped out of school, Darry works two jobs, and Johnny has adapted to life on the streets; Two-Bit, Steve and Dally are already well on their way to becoming legitimate hoods. But they all see Pony as an outsider: Being the youngest and the smartest, they have hopes that he will not turn out like them. Quiet and sensitive, Pony is not as tough as the others, and his friends hope that he stays that way. Two-Bit's quote--that Pony not "get tough"--is a plea to follow his own instincts, and not the get-tough attitude that Dallas Winston took to his early grave.
He doesn’t want Ponyboy to act tough because he knows he’ll get injured or hurt.