Recently encountered this in vocabulary:
留守番電話 (“answering machine”)
which is composed of
留守番 (“housesitting”)
and
電話 (“telephone”)
This made me chuckle because it makes so much sense and yet is so far away from the English. The image of a machine housesitting your phone for you is kind of funny too.
One of the simple pleasures of learning Japanese.
Any vocabulary that tickle you?
大人. An adult really is just a big person, after all!
After all this time 手首 is still my favorite. It sounds exactly like what you’d say if suddenly you completely forgot how to say wrist. Ah! I twisted my… uh, hand… neck?
Recently learned 毛糸 which made me laugh since I was able to guess it on the lesson page before I even read what it was. I’m also fascinated by 下町 since from what I’ve been able to find it developed independently of the English version of the word and yet ended up being so similar by pure chance.
Yes! That’s a good one too.
金玉 but that’s because I’m a man-child lol.
Gold, Ball. It means Testicle… from WK level 5.
Since when is the mere word “testicle” NSFW? It’s on WK, too…
I believe it is a fine, scientific word, but some more conservative people might feel differently, cause heaven forbid someone uses a word that in anyway describes reproductive organs lol.
鼻くそ made me smile when I learned it. It’s “nose sh*t”, which, if you think about it, is exactly what snot is.
I like 劇的, simply because it’s fun saying, “gekiteki”. I also picture an incredibly dramatic robotic gecko, it’s all fun and it’s one word that’s stuck with me immediately after learning it
That reminds me 飛行機 - fly go machine. Gets me every time.
I really get a kick out of the fact that breakfast, lunch, and dinner are just:
Morning rice あさごはん
Noon rice ひるごはん
Evening rice ばんごはん
(Dunno the kanji yet)
海 (ocean) + 賊 (thief) = 海賊 - pirate 
My absolute favourite is this:
痴(ち, stupid) + 漢(かん, Chinese) = 痴漢 (molestation, groping)
So a stupid Chinese creeper is responsible for groping innocent Japanese girls in crowded trains! 許せない！
You will often hear or see this warning in public transport in Japan:
痴漢は犯罪です！
(Groping is a crime!)
I really love that a caterpillar is 毛虫 (fur+insect).
So fluffy! 
it is so memorable, lol. It was one of the first that made me lol out loud.
Mine right now is 海王星 or Neptune. Its Sea King Star, which first made me think of a purple seaking pokemon whose name is Poseidon. So I giggle because that is a ridiculous first impression & cause its just kinda cute.
When I came across the ones that have been mentioned, I was yeah makes sense indeed, but… 金玉 is indeed the one that really made my day (so to speak)! 
Actually 漢 is used with the meaning of “man” here. 
the reverse gender version of that word is 痴女
The vocabulary that recent made me tickle is:
桜肉 – horse meat
At first, I’m like “wtf?”
It helps that its so weird and I think its burnable already.
So I googled the reason and this is the first entry:
馬肉の色が桜色であるからや、桜の咲く時期の馬肉は冬の間に草や殻類を沢山食べて脂がのって美味しいことからといわれる。
It says that maybe its because horse meat has a pink color like cherry blossoms, or that horse meat is most delicious during the season when cherry blossoms bloom.