what would iran's response be if azerbaijan starting screwing with iranian held azerbaijan?
Depends, but it could be very strong. Azeris might be the second-largest ethnic group in Iran, after the Persians (there are many more Azeris in Iran than in Azerbaijan), they live compactly around Tabriz and they can potentially be part of a non-negligible secessionist movement (during the 20th century there was a brief moment when under Soviet influence Iranian Azerbaijan came close to being split off). An interventionist Azeri regime would be flat out unacceptable to Iran.Azeris are over ten percent of Iran's population, and I'm very sure they are the second largest ethnic group there. Have a look at the recent presidential election results in Iran btw - with political lines badly defined, most candidates (all of them really, though the effect is less marked with Karroubi and Rafsanjani) had very strongly defined regional strongholds - although ethnic issues did not apparently play any role during the campaign. One candidate wound up as, effectively, the Azeri candidate, winning all three Azeri provinces, two of them by large margins, and poll next-to-nothing elsewhere. I've forgotten the name.