It is leetified( I was young god damn it) word "Gurķīts"(Proper term is "gurķītis"), which is derived from the Latvian word "Gurķis", which means cumcumber, while "gurķītis" is more of a cute word. Like, for example, the latvian word for bear is "Lācis", but if you want to use the word in a more friendlier way, say a teddy bear, then you use "Lācītis", or cat("kaķis") and kitty("kaķītis"). It can be done for almost all nouns.
Anyway, the reason for calling myself cucumber is lost to me, as I first started using it 3-6 years ago, as previously I used to go by "mustang" in my Runescape days. I got sick of it, so when I stopped playing Runescape and started pubing around in CS 1.6, I switched to Left4Gurkis, and then it went trough several variations, until it became The_Gurk1s, which is the most used variation. There was a brief period I went by Gurk4ever, but in this brief moment I made my Youtube and my Wargaming.net(WoT,WoWp) account.
Despite this, "Gurķis" is somewhat popular name, so for the past year I have switched over to using "SunnyBittern" as my handle, derived from the South American bird Sun bittern. So most places where I have "Gurķis" or a variation of that is a place I registered before December 2012.