Closest I've got on my list is the same situation, but the priest imagines himself telling the guy to use a religious statue on himself: https://www.mangago.me/read-manga/ijimetaihodo_aishiteru/mf/v01/c004/
I also have (among many different objects) various fruits and vegetables, several bottles and pens, a crapload of guns, a roll of film, a rubber duck, two traffic cones (yes, two different manga), but no cross. Imma gonna sit here in case it shows up (● ̄(エ) ̄●)
(Another I have is someone inserting a riding crop into a priest)
I'm so glad I could help!!! And here's the list with all those other stories: https://www.mangago.me/home/mangalist/92534/
this story was weird as fck and i was half out of it when reading, Li (love interest) was living 2 lives 1 as a family priest and other as a normal guy, mc goes to his confession booth after a few times and Li tells him to fck himself with the cross---- i dont know why my brain is making me have the urge to find it, its an itch that needs a scratch