With regards to Sheriff Lamb's general disdain for the people of Neptune, the Sheriff's anger is most visible when dealing with those who Lamb feels are cowardly, weak-willed, or who generally wallow in a sense of victimization in terms of being unwilling to stand up for themselves.
In the third season episode "Mars, Bars", Wallace reminds Lamb of a time when Lamb told Wallace to ask the Wizard for courage.