Even if you were angry, you shouldn't have said something like that.
Literal
Even-if-たとえ you [subject-が] angry was [even-としていても], that-kind-of thing [object-を] say should-not-have.
~としても ('even if X, even granting X') is a concessive pattern. The embedded clause uses past tense 立腹していた ('was angry') to frame the counterfactual. ~べきではなかった is the past-negative of ~べき ('should not have done X'). A mild rebuke.