Bastardization of vegetarian used for dry humor. The idea is that the user has never heard of vegetarianism and thinks he is inventing the word for it when somebody says that they don't eat meat.
The humor comes from oversimplification, implied ignorance, and laughable wordcoinning. It also kinda sounds like Unitarian, implying a quasi-religious respect for vegetables.
Dude: Have some chicken fingers.
Loser: I don't eat meat
Dude: Chicken is barely meat.
Loser: I NEVER eat meat, I'm a vegetarian Dude: Oh, so you're like a vegetableitarian?
Loser: ehhh...I guess.
Dude: Sorry, I didn't mean for you to go against your "religion"
Loser: (huhhh?)
an emo vegetarian; one who abhors meat and cries at night because animals are killed in factories in chicken wire cages where they are prevented from grazing in green fields and loving one another; one who once tried to go vegan but was unable to make it past one month because of these two things called chocolate and cheese
1) Why don't you eat lambchop you little vegetabletarian child? (mean, derogatory)
2) Hey, don't talk to her about chicken, she's vegetabletarian! (supportive, analytical)