The Battle of Alesia, the battle that finally sealed the fate of Vercingetorix. The Siege x 2. Caesar had besieged the city with fortifications, and was waiting the Gauls out, when another, larger, Gaul army besieged his armies. In other words, Caesar's legions were trapped between two Gaullish armies, a sort of Roman donut between them. He still mopped the floor with them.
The really awesome part is that Caesar predicted that the Gauls would have another army coming to aide Alesia, so he built fortifications around his own fortifications and thereby protected his army from the second assault.
After having dealt with the Gauls, he decided to teach the Germans an object lesson. he had his engineers build, in record time, a bridge across the Rhine river, crossed, cleaned some German clocks, and then had his troops march back across the Rhine, tearing the bridge down as they went, with the implicit promise that Caesar could and would repeat the process should the Germans cause trouble. His own account is overindulgent about the punitive episode, it ended with a Tactical Withdrawal, as soon as he learned he was facing the powerful tribe of the Suevii and not a lesser one he returned to his quarters.
After Pompey fled at the Battle of Pharsalus, Caesar pursued him, but returned when a messenger told him that, once Pompey's armies had been defeated, his own armies had begun to slaughter them mercilessly. Caesar returned and announced to his men (something along the lines of): "There has been enough bloodshed today; the next Roman you kill will be me!". Pompey's remaining armies were so impressed that many of them joined Caesar after that.
Caesar did a lot of Bad Ass things in his day. Like telling the pirates who took him for ransom that they were demanding far too little money for him. Then he told them that once he was free he would hunt them down and have them all crucified. He did.
He also refused to give in to Sulla's demands that he divorce his wife when Sulla had him captured. At this point Caesar was far from a prestigious person and had no reason to believe Sulla would do anything other than torture and/or kill him if he refused. He still refused. Sulla was so impressed, he let Caesar live.
During the senate debate on what to do about the Catiline conspirators Caesar received a letter. Cato demanded that he read it out-loud but Caesar refused. When Cato accused him of being in cahoots with the conspirators and that the letter would prove it Caesar calmly handed the letter over to Cato so that he could read it out loud in the senate. Turns out the letter was not from Catiline or one of his conspirators - it was a love letter from his mistress Servilia... who so happened to be Cato's sister.