Chandler enters the room looking very excited about something. When his friends asks him what he's been up to, he mentions this woman he's been talking to through the internet. He says he understands he can be sometimes a little bit defensive and quipy, but she was the first one among the people he knows that had the courage to call him on it and say and he should cut it out and get real. But wait, do you know what to call someone on something means?
When you call someone on something, you're calling their attention to something bad about them that they might ignore or choose to avoid. In the case of Chandler, as he said himself, he's always been someone very defensive and needed someone to tell him in a very straightforward way that he should change that. He was happy the his "virtual girlfriend" called him on that. Suppose you're someone very shy around girls and one day a close friend of yours calls you on it and says you should stop that, try to be cool and understand girls are not that scary. Your friend called you on your shyness, he called you on the fact you're just too shy and may be over thinking the way you behave around girls. He wants you to change for your own good. That's it for today guys. Take care!