It was a peaceful occupation of Greek facilities used to facilitate the Israeli flag carrier to perform it's duties, in Greece. Delaying flights, ships docking etc are legitimate demonstrations as long as they are done peacefully. Think Shalit's family walking around Israel causing traffic chaos, same proncipal in an attempt to change the behaviour of the Netanyahu government. But the thing really grating for you I would presume is that no violence was used, in a democracy that is legitimate protest, and Greece is the cradle of democracy. Hopefully this type of protest will grow.
Army: Blast in Korean DMZ wounds two South Korean soldiers (Reuters)
from the article: Anti-Israel protesters delay El Al flight in Athens