Idolatry has a special place in Jewish law along with bloodshed and promiscuity as being one of the three cardinal sins. Whereas in the rest of Jewish law we attempt to find leniencies to accommodate people, we are much stricter in regard to this area. It makes sense, since once a person can create G-d in their own image, then everything else becomes fair game.
There are three areas of consideration for this question: Halacha (Jewish law), official doctrine, and popular belief and behavior.
The Torah forbids making images, be it of G-d, other gods, or a whole host of natural phenomena, basically anything that could be worshipped. This is the second of the Ten Commandments and is a prohibition repeated many different times throughout the Torah. It would seem then that there should be no leniences.
There are two possible areas where one could come to find a reason to permit this: people's belief systems and the status of the object itself.
The Rema, the Ashkenazi (Eastern European) authority for Jewish law, found a slight leniency in the area of Yayin Nesech. There is a prohibition to drink or even derive benefit from non-Jewish wine because a non-Jew might have poured some wine as a libation to their god. However, the Rema says that pouring wine to idols is not normal by non-Jews and therefore selling the wine would be okay (Yoreh Deah 123:1).
According to Venerable K. Sri Dhammananda Maha Thera, Buddhists pay respect to the images of the Buddha and the Bodhissavah but don't actual worship or ask requests from these images. They are revere as great people and what a Buddhist does by praying in veneration of what he (the Buddha) represents. They use the object as a focus of concentration during meditational activities and such but do make offerings as if the real teacher is standing before them. The comparison made by Maha Thera is to that of a memorial, although this memorial seems to have some kind of living properties to it.
I have however seen how Buddhists behave with these statutes. They believe bad things will happen to you if they break, meaning they subscribe a belief that supernatural powers reside in the object even as official Buddhist doctrine would negate such beliefs. It would seem that regardless of what dogma states, Buddhist statues have the status idols in every sense of the word.
Then there is the status of the head itself. Here we are dealing with a plastic head. The assumption is people wouldn't worship things like plastic or plush toys. An idol should be something significant like nice stone or gold. The Shulhan Arukh (Yoreh Deah 141:1), the codification of Jewish law, says that statues made just for beauty can be used. That's why stuffed animals and G.I. Joes are okay. ( Barbies are creepy and shouldn't be brought into the house, though my wife argues.) The Shach, a Polish commentary on the Shulhan Arukh, argues and says any figure of a person should be forbidden. Certainly the image of an actual deity should be forbidden.
However, people do in fact worship plastic statues. The statues sold at botanicas, the stores that sell images of Catholic saints and paraphernalia are in fact the object of worship. This is especially true of the Narco-Saints, figures that have been deified in Mexico as a response to the horrific situation in some cities but are now found in the United States, whose worship is growing like wildfire. Their worship cannot be written off as the actions of a few crazy people but a renewed enthusiasm for a new form of idolatry that is a fusion of Christian and Mesoamerican religious traditions. Moreover, the types of actions they engage in to worship these saints is varied, and the pouring/offering of wine to idols might be going on there. In that case, we make what is called a lo ploog, a rule that says that if someone is true in one case we extent that rule to all cases that are sufficiently similar.
The conclusion: the neon Buddha head should stay at Ikea. If you already bought one, I can't say whether or not to get rid of it, because it would seem that it is in fact made for decoration. It requires further thought.
Answered by: Rabbi Name Withheld By Requet