Iran is anti-USA solely because the USA is anti-Iran.
They've made a number of attempts to normalize relations but the USA just keeps going back to tarring Iran as evil before long.
Yep. Anti-usa sentiment (and posters here are seriously overestimating any such sentiment imo) was originally rooted in the reaction to the CIA-backed coup that overthrew a progressive, democratically elected prime minister and effectively installed of the shah, regarded by many as a despot, who was of course on fabulous terms with the US.