I don't get this one.

I don't get the santa-part either, but the point of Rin breaking Miku's concentration is hilarious!

"吹いたら負け" game?
(If you burst out laughing, you'll be the loser)

not just satisfactory, ROYALLY SATISFACTORY!!!!!!!!!!!!!

I lost..

Maxwellgarding said:
I lost..

the game.

BA

I did a spit take

Brightlight said:
"吹いたら負け" game?
(If you burst out laughing, you'll be the loser)

i.e.
You Laugh, You Lose.

sgcdonmai said:
i.e.
You Laugh, You Lose.

Then by that logic I have already lost. Forgive me... [Dies]

FIRST PANEL
すうー *suuu–*

SECOND PANEL
ぷくっ *puku–*

THIRD PANEL
バッ *ba–*

LAST PANEL
サンタが子供たちからプレゼントを守ろためにあみだした必殺技！ Santa ga kodomo-tachi kara purezento o mamoru tame ni amidashita Hissatsu-Waza!

“A Deadly Technique that Santa devised to protect gifts from children!”

ズギャーンッ *Zugyaaaan–*
ギュルルルルル *Gyurururururu*

ロイヤル • サティスファクション “Roiyaru • satisufakushon” “Royal Satisfaction”

ボフッ *bofu–*

必殺技 ひっさつわざ Hissatsu-Waza
1. "killer technique; surefire assassination method"
2. "special or lethal move, usu. one unique to a certain fighter or fighting style, ​Martial arts"

必殺 Hissatsu – “bringing certain death; deadly; knockout (blow)​”