About

Bojler eladó is a Hungarian phrase, meaning boiler (water heater) for sale. It's used as a comment by Hungarians when they see a Hungarian reference on a popular international platform like 9gag or reddit, where it's a rarity that this small country is mentioned. Other Hungarians often hop on the joke, and ask the commenter about the quality of the boiler, its price, etc.

Origins

It is a punchline from a Hungarian joke which can be translated as follows:

Kovács dies. His widow asks the best friend of the family, Szabó, to request an obituary notice but a short one so it would cost less.
Szabó goes to post the obituary notice and dictates the following text: "Kovács died."
The administrator looks to him surprised: "Is it that short? The price is the same up to 5 words."
"Alright fine: Kovács died. Boiler for sale."

The phrase refers to the increasing sales of boilers after hot tap water was introduced to many rural households. Since it was before the Internet, people advertised their boilers on flyers pinned to lamp posts, walls, etc. Given the surplus of boilers for sale, it became a useless addition to advertisements of other things for sale, e.g. "Motorbike for sale (insert detailed description) Btw, boiler for sale as well."

Spread

When the time of online forums has come, this funny addendum was used at the end of long posts where a lot of topics were covered, as just to add another item to an already long wall of text, for fun. Or as a comment to such long post to joke about its overwhelming amount of text.

Then the phrase was used with the same intention on international forums and other sites, leaving foreign people clueless about its meaning. Now it's just to confuse non-Hungarians, it is commented below any post mentioning Hungary or something related to it.