The full sentence is 「ちょっと こいや」.
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4Since no one has mentioned it in his answer, I am going to mention it here. It is the tough guy's imperative. Everyone says "Come here." in English, but only a limited number of people would say 「ちょっとこいや。」 in Japanese. – l'électeur Mar 19 '15 at 7:23
It's not a word on its own, but a combination of 来い (imperative "come") and や (see #3 in this dictionary entry).
As l'électeur pointed out in the comments, it can be understood as a "tough guy's imperative."
As l'électeur said, it definitely shows tough guy's commanding nature. For example consider the following statement:
そんなの忘れてちょっくら晩飯でも食いにこいや。
Forget your troubles for a while and come and have dinner with us.
In the statement above
ちょっくら means a little
晩飯 or ばんめし means dinner
食い or くい means eating
As you can understand from the context, the speaker's statement has somewhat demanding/commanding nuance attached to it. I think if you understand the nuance, you will understand how and when to use it.
This means come here and it is quite casual.
