You don't go "ka-boom" on Yuuka Flan, you just don't.

Dog house for Meiling ?

I can't think of any reason to utter "gyu" as an exclamation instead of a normal word, so I'm going to assume she was about to start some sort of cow-themed insult since there are very few words that start with that sound that aren't cow-related and all of them make even less sense.

Ka-blooey

Flandre Scarlet almost said:
Just die already, cow-tits.

Just to whomever did a slew of down-voting to these comments:

These comments are harmless, constructive and funny; there is nothing "down-vote worthy" about them.

Calm your own cow tits down instead.