I have a thing for words that aren't used very often, and I find some older english words really satisfying. Some of my favorite words are;
"Indubitably"
"Irksome"
"Hippopotomonostrosesquippedaliophobia" (though I am not sure if this is actually real or not, it is allegedly the word describing the fear (phobia) of long words, ironically)
"Unequivedly" (can't spell that word on top of my brain)
in german my favorite word is "Garnelen"
It just sounds cute
In my mother tongue (Norwegian) my favorite word is "Rumpetroll".
It directly translates to "butt troll" but it really means Tadpole.
I find that really funny, especially considering tadpoles looks like sperm.
In Turkish my favorite, and only word I know, is "Gegirmec" which means fart
I played a game of Dota 2 and said "I farted through my mouth" as a joke eluding to I just burped.
One of the players were very confused and when he realized what I said he simply just said "Ah, Gegirmec!"
I thought that was really funny, and it stuck with me.
In Japanese some of my favorite words are
"Ikanimo" it means "indubtiably", it is an older word and isn't used very much in current time, but I personally feel it has a different and useful nuance opposed to the more commonly used "tashikani" or "sou"
"Rairairakuraku" I heard this word in a song, I don't remember the meaning very well, but it was something about possession of a spirit n' stuff. I just thought the word was really overkill.
There are probably more words I really like, but at the moment those are the ones I can think of