Jimmy "The Neck" is Frankie Fusilli's bodyguard.
In The Sims 2 for Nintendo DS, he comes every now and then takes people hostage and makes the player pay him money and then releases them. He sometimes comes and terrorizes the citizens of Strangetown, and he will call in more friends such as Reginald "The Wrist", Tommy "The Toe", and Freddie "The Face". In this game he cannot be socialized with and therefore cannot be befriended, unlike in the GBA version.
In The Sims 2 for GBA, he is the one that gives the player the water gun as a reward for helping him out. Jimmy appears to have a very low IQ and some kind of short memory but he is way more friendly than in the DS version.
His secret is that he teaches jazz to children in his free time.