Gascibating is a bastardisation of the word "fascinating". It may be used in two ways.
1) As a sarcastic response of false interest.
2) As an enthusiastic and silly response/descriptive word similar to "fascinating".
Jon Martens: I just ate some cheese.
Keiper: How gascibating.
Kyujuni: In Canada milk comes packaged in plastic bags.
Moinex: That's gascibating ! Although not as gascibating as Allenby's giant inflatable hands !