Vampires carry a Beast inside them. Under extreme circumstances, the Beast sometimes takes total command of the vampire. This is referred to as “Frenzy”.
A frenzied vampire will usually try to drink whatever he can, avoid whatever he can't drink and destroy whatever he can't avoid.
The Frenzy continues until either the Beast is sated enough for the vampire to resume control (Vitae is great for this purpose, but carries other complexities), or until the Beast is stopped, which means either Torpor, or destruction.
Obviously, the Frenzy is a great danger both to the afflicted vampire and to the the Masquerade. Frenzy is very much frowned upon by the Camarilla generally and by the Ventrue especially. It is the mark of childer, too weak to withstand their Beast and too stupid to keep it happy.