* An understated one, but way back in Season 2, Don is being targeted by the Russian mob, and it's made clear they will go after those closest to him as well. Two men show up at Charlie's lecture, and he manages to send them away without inciting panic. That he is clearly under tremendous strain just shows how awesome he is for keeping his head.
* In the Season 6 premiere, Charlie manages to figure out the exact position of a sniper using math, ''while being fired on''.
** A far cry from his situation five seasons earlier in "Sniper Zero".
* In the Season 5 finale:
-->'''Amita:''' My book will be called "My 3 days with a ''computer illiterate''!"
* Charlie weaponizing an MRI machine on an assassin in "Janus List".
* Charlie talking to the man that stabbed Don:
-->'''Killer:''' Is it worth your life?
-->'''Charlie:''' It's worth this moment. Meeting the man who stabbed my brother.
-->'''Killer:''' Your brother? The FBI agent?
-->'''Charlie:''' *drops the millions of dollars of diamonds the man had been looking for as the agents swarm in*
* There's an interesting one in the Season 1 episode "Dirty Bomb". The FBI has captured the three men involved and none of them are talking. Charlie then decides to apply Game Theory and so the FBI puts all three men in the same room (against typical procedure.) He draws a chart and calculates risk values for them, with the higher numbers meaning the person has more to lose. Up until now, the leader remaiend cool-headed and confident his buddies wouldn't talk. Cue the OhCrap faces when they see how much they have to lose, especially the leader's foster brother, who stands the most to lose by not talking. The leader himself loses his cool when he realizes the effect this has on his co-conspirators. Ultimately, the young man comes clean and reveals the location.
** Don himself lampshades it at the end of the episode.