What does 「ひざっこぞうをたたいてみるよ」 mean?


This is a line from the song 「結婚しようよ」by 吉田{よしだ}拓郎{たくろう} ([youtube
link](https://youtu.be/ryutpbPwrz4?t=136))

Relevant piece of lyrics:

> 雨が上がって雲のきれ間に
>
> お陽様さんが見えたら
>
> **ひざっこぞうをたたいてみるよ**
>
> 結婚しようよMMMM

[Source](http://www.utamap.com/showkasi.php?surl=36495)

When I googled it, I came across 膝を叩く which seems to be used when you "get"
something (an element of surprise where you tap your knees to show it) but I
don't think it has that meaning here.

Also, I could not find a proper meaning for ひざっこぞう but I could find a meaning
for ひざこぞう (kneecap) which means the っ is probably used for emphasis.




First of all, your interpretation of 「ひざっこぞう」 is correct.

ひざっこぞう ＝ ひざこぞう ＝ ひざ ＝ most technically, ひざ頭{がしら}

By adding the こぞう（小僧）= "a little boy", it personifies the word 「ひざ」 =
"kneecap".

Regarding the meaning of 「ひざっこぞうをたたいてみるよ」, I have always thought (in Japanese,
of course, as I did not speak a word of English when this song came out) that
it meant something along the lines of " ** _I'll slap my thigh (and cavort
around.)_** ".

In other words, it means to me "I'll be saying 'This is it! I've gotta marry
her (or propose to her)!'"

