Norse Mythology's Vanir were a race of fertility gods, who spent their days making the world flourish with plants and children... Oh, and they almost destroyed the Aesir.
Nymphs were usually kind and flirtatious, but piss one off and you're likely to be drowned and gutted. Or, saddled with a curse so horrible that you'll wish you were drowned and gutted.
Most people seem to think of Demeter as peaceful and calm, the goddess of the harvest and growth. One of the lesser known myths shows us just how awesome she can be: a King cut down her favorite tree. So she got one of her handmaidens to fetch Hunger, and sicced her on the King, until he ate everything in his city, spent and sold everything he had, even his own mother, and then ate himself.
Not to mention the whole "If I don't get my child back, I can and will kill everything on this planet" thing.
There is also the fact that Hephaestus, the Smith of the Gods, while nicer than the rest, is best not to anger him. More known examples include the Golden throne incindent and the Golden Net scandal.
Jesus and "the cleansing of the temple". This is a guy who was literally the poster boy for patience and forgiveness. But everybody has at least one thing that really burns them up and makes them want to break something/someone; for Jesus, it seems, it was taking advantage of poor and ignorant people in the name of God (the corruption in the Jewish church was along the same lines as the selling of indulgences in Martin Luther's time). When he saw what was going on, he just stood there, looking around and emanating so much anger that he didn't even have to raise his voice for everybody in the temple to know that some serious shit was about to go down if they didn't get out of there. He flipped over a money-changer's table, and the priests and merchants ran like hell. Some variations state that he busted out a riding crop and went to town on all the tables and stuff sold there. This was preceded by cursing a fig tree that was out of season and didn't give our Savior fruit to eat.
And then there's the prophesied Second Coming. The first time Jesus came, he was generally peaceful. The second time? Not so much. There's a reason he's called both the "Lamb of God" and the "Lion of Judah".
Many verses, especially Nahum 1:3, gives us the description that God is "slow to anger", but when evil strikes, He will stop at nothing to punish the evildoers.