You might want to read up on the Iran-Iraq War. The Iranians have quite an appetite for war and have proven themselves capable of fighting a long, drawn out war of attrition.
That being said however, the use of this language is regrettable, especially after Pakistan hosted the Iranian FM and assured him of full cooperation in this regard. With relations already hanging by a thread, any such untoward incident will only drive Pakistan and Iran further apart which would also harm Iran's own interest since Pakistan is the few remaining neutral countries in the Iran-KSA split.
Such threats are to be expected though when we let an incident like Chaman go unpunished. Pakistan's response should have been very strong and very visible. Simply accepting the Afghan's ceasefire and sharing a table with them a few hours after they mercilessly gunned down 12 unarmed civilians and 2 FC men was disgraceful.