Funny/strange Kotowaza

In a recent drama (Hotaru no Hikari, ep 5, 4:18), the following kotowaza is used:
へそで茶を沸かす (Heso de cha wo wakasu)

It means to boil tea on your stomach/navel, which apparently means "It's so funny I could laugh" in Japanese.

So basically, the conversation went:

friend: <says something stupid and ridiculous)
woman: HAHAHA..LOL...yeah whatever...that's impossible...I could boil tea on my tummy.....

It seems to have a sarcastic tone to it.
Anyone else know of any kotowaza that you thought was funny/strange when you first heard it. I would have NEVER guessed the meaning of this phrase on my own.

Thanks.