A chance to visit a place probably/hopefully unique in the whole universe.

A trivial or insignificant item and potentially a nuisance. 


To be used with irony or contempt ideally.

In the phrase ti masskaraliki bou ebatha (What a masskaraliki I have suffered) the word is being used ironically and the speaker may be referring to a considerable personal tragedy. (Rolling the thiplowgambinon, grandma being discharged home from the hospital etc.)
Non-ironic examples of times when the word masskaraliki might employed include when the police are breathalysing you in the event of you being caught driving in a state of what the armed forces describe as "tired and emotional",  One looks suspiciously at the device and announces ti einai doudoh do masskaraliki, reh?, effectively "what is that stupid little thing?".  Its not going to change anything '(unless your Greek impresses the police officer) but hopefully you will feel at least you got a shot in before they slap on the handcuffs.
Otherwise when your yinaiga (type 1) finds an unidentified earring in the your jacket pocket, you might be attempting a pre-emptive strike to avoid a grilling.

If one wishes to be more emphatic about the triviality of the subject under discussion, it may be referred to as a batsariji


Better still, drive sober and give the jewellery to your wife..