Maybe donating for Malaria would just have been to silence Cueball's conscience, and Megan's comment made him realize that he really wanted to spend all the money on games. It could also be that Megan's snide denigration of Cueball's act of charity as inadequate and self-serving has dissuaded him from any act of charity at all, if this is what it gets him. In any case, it seemed to give the opposite effect than intended.
Supposedly these kinds of conversations happen to Randall on the internet, so a good way to avoid them would be to quit participating in stupid and meaningless discussions there.
The reference to 0 internet arguments in the title text is to the zero-sum game of Game Theory. Megan is suggesting that the overall utility of giving $10 to charity is poor (whether or not this is actually the case), therefore Cueball cynically decides that the utility can be increased by spending the money on himself. "Internet" presumably because such discussions frequently happen on the Internet where the rules of logic are somehow different.
- Cueball: I'm going to buy this $10 game I want, and I'm donating $10 for malaria eradication.
- Megan: If you actually cared, you'd skip the game and donate all $20.
- Megan: What's more important? Games, or mosquito nets and medicine for kids?
- Cueball: I think I'm going to buy these two $10 games I want.
- Friend: Cool; which ones?