He gets too emotional sometimes and takes offense easily.
When he killed one of the brood, he took it very hard knowing he killed a human who did not know what was coming to him/her.
When he thought Jamie Madrox was dead, he blamed himself for allowing Haven to try and heal him from the Legacy Virus, which ultimately lead to failure. He remained unproductive until the reassurring words from Polaris and/or the possession of Malice.
He has maintained on and off bouts with Cyclops, whether it be reputation issues (i.e. Havok being outshined), the mistreatment of Madelyne Pryor, etc.
And who can forget he tried to open the trick maynonaise jar made by Multiple Man by blasting it.