Well I don’t read one piece, but here are some himbos for ya:
http://www.mangago.zone/read-manga/rumspringa_no_joukei/
http://www.mangago.zone/read-manga/the_good_teacher/?nqS9
http://www.mangago.zone/read-manga/wolf_in_the_house/?JXDr
http://www.mangago.zone/read-manga/kore_wa_koi_ni_fukumare_masu_ka/
Lol your criteria being luffy is funny and not sure if these semes are that idiot but here are some funny idiot semes ^ ^
http://www.mangago.zone/read-manga/sonna_me_de_mite_kure/
http://www.mangago.zone/read-manga/kino_to_yano/
http://www.mangago.zone/read-manga/kimi_to_ishin_denshin/
http://www.mangago.zone/read-manga/doushitemo_yaritakute_gakuen/ everyone and everthing in this manga is dumb beyond reason lol
halo ! please gimme a BL where the seme is as stupid as Luffy ( one piece )