ok so ive laughed about this to a couple of my friends in the past but when i was talking to my friend sei we realized that we hadnt actually seen a post about it on tumblr before. so here i am!
as said in the title luffy’s laugh is actually a pun, or more specifically a meat pun. we all know how much luffy loves meat. he actually yells about it so much that if u watch the anime subs u probably noticed very early on that にく(niku) is japanese for meat.
as for luffys signature laugh he always goes “shi shi shi” which is often just translated as “hee hee hee” in the manga (at least in the translations i read). now heres where we get to the pun itself:
in japanese the kanji for meat is 肉 which has two different readings, an on-reading and a kun-reading (there is a difference between the uses of each but that isnt rlly important for this pun so im not going to explain it.) now, the on-reading for meat is にく (niku) but the kun-reading is しし (shi shi) so when luffys doing his signature laugh it is literally a meat pun!