You have to start earlier than that. In the 1950s, Iran became a brutal dictatorship under their Shah ( who got there with an Allied-sponsored coup during WW2) via a CIA and MI6 sponsored coup against the democratically elected PM, who wanted to nationalise British oil interests to fund social programs and improve Iran. The Shah brutally supresed opposition, until one day it became too much and in the 1970s a revolution by a communist and Islamist coalition overthrew the old regime ( the islamists came up ahead and Iran became an Islamic Republic). The US has been against them from that moment on, and Iran has hated them for enabling the Shah, and continuing meddling ever since. ( Bar a small and very illegal episode known as the Iran-Contra affair, where the US sold weapons and spare parts to Iran in exchange for off-books cash, which was funneled into the terrorist Contras in Nicaragua, to circumvent US Congress restrictions on help to the latter)

It's fascinating reading, i encourage you to look up the details yourself.

Presumably

A) They don't want to play economic ball with Uncle Sam.

B) The country can't be conquered by conventional means so can "act out" as much as they like.

C) They aren't really that bad, US propaganda is just really, really effective.