Hong Kong/Iceland is a common pairing between the characters Hong Kong and Iceland. It is also known as HongIce or High School Boys, due to the Gakuen AU being the most used in fan works for these two. It is also addressed as Hot n' Cold. (The origin is still unclear but it may be an interpretation of Iceland's hot and cold personality aka Tsundere, Hong Kong's warmth and Iceland's coldness or a Lady Gaga song reference.)
Interaction
From the few interactions they ever had, the most appealing one is during the Halloween Special (which was only released in Japan through the DVD Blue-Ray edition). In the event, Iceland joins the chain of countries who notices that something is amiss. He is seen both with Hong Kong in the same panel leaving hints about the the disturbing content that is missing.
After the sudden appearance of America costumes as Batman with England at his side on the stage, Iceland finally notices that the "empty feeling" is England with his constant action of pointing at weird things. Hong Kong then proceeds to confront him about this, asking him about how he's feeling at that current moment. This may be a tease since Hong Kong is smiling and has an amused expression on his face; a rare occurrence for the former nation and Iceland is seen trembling, probably by embarrassment of being caught.
Fan Speculations
Fans of this pairing usually described Iceland as a Tsundere, a character that acts cold and volatile towards the person they have affection for while being affected for them at the same time. The reason is because of Iceland's canonical personality of being cold but has a hot side that is not shown to due to him being embarrassed. This suits the tsundere traits perfectly and makes Iceland as one of the tsundere characters in the series.
Fans interpret this pairing as a match between two characters that both feel isolated in their families and both want to stop being treated as children. Most fanfictions featuring these two are usually set in the Gakuen Alternative Universe where they both are teenage school boys. Sometimes, they both have dysfunctional families or just the normal types. They both are known are rebels and always keep their siblings on the edge of their seats.
Even though they actually don't have any sort of historical relations in real life, the pairing is very widely-known in the fanbase.
Moments
Halloween Special
*2013/2014 Halloween
Blu-Ray DVD Special
* Halloween Event 2011 / Halloween Overflow