How serious is Iran's threat to disrupt shipping in the Red Sea?

Some call it the Gate of Tears. Bab al-Mandab in the Red Sea wields importance as a global shipping artery. This week, Iran's Revolutionary Guard threatened to use the strait as its next front in the war with the US. It says regional energy exports are 'either for everyone or for no one'. Such a move would mean relying on its Houthi allies in Yemen to block the shipping route. Iran's warning comes amid an escalation with the US, which has endangered last month's agreement. What would it mean for a volatile region -- and the global economy?