I think the question is not so much what they can do to YOU, as you so elegantly phrased it* (suffice to say that anything bad Iran could do to U.S. would likely either be universal, i.e. muckin’ with the oil supply, or could be targeted at any country in the Western world, i.e. state-sponsored terrorism), but why they should want to.
Look at what Iran has done recently. Made some outrageous statements and (potentially) started on the long and rocky road to possessing nuclear weapon capability (if they are lucky, in five years, at tremendous costs, if they want to make weapons and have the required technology). And what did it gain them (or, more accurately, the current Iranian president): International recognition, both positive and negative, some concilatory approaches by Russia, and popular support at home. In other words, they have learnt that overblown political statements=treat.
But what if they were to actually start rocking the oil boat, or sponsoring terrorism? The whole world, both Western and Arab, would be on them like a ton of bricks. OPEC has no desire to see the currently very-favourable oil market damaged, and terrorism would make them TRUE international pariahs plus give an iron-cast excuse for military intervention. Even if they could ride these waves, what would Iran gain from this? The leaders of Iran may be bigoted, or even stupid, but they are not insane. Meanwhile, their domestic mismanagement has already eroded the support the current adminsitration gained during the last election. The only sure way to provoke Iran into stupid and reckless acts now would be- you guessed it, massive foreign over-reaction. Such as invasion.
In conclusion? Iran can do little. And what they can do, they won’t. But any attempt to stop them doing these things? Might cause them to consider them.
*I am reminded of a joke. The lone ranger is surrounded by indians, with no chance of escape. He turn to Tonto, and says: “Well, Tonto, looks like we’re done for.” Tonto replies: “What do you mean WE, white man?”