And this is why protagonists should never be allowed to name things/beings.

I remember the isekai manga where the protagonist is unable to understand people's names so he gave them nicknames instead

Could you be so kind to tell me what the name was? Plzzz(๑•ㅂ•)و✧

Sadly I forgot the title already but I remember his companion was a wizard reincarnated into a frog

Hmmm thank u I'll look hard enough so hopefully I'll stumble on it one day

Then I believe you are re talking about this one:
http://www.mangago.zone/read-manga/ore_to_kawazu_san_no_isekai_hourouki/

You also have the one when MC purposely give them horrible nickname that they all hate:
http://www.mangago.zone/read-manga/tensei_kyuuketsukisan_wa_ohirune_ga_shitai/

Yes, that's the one! I've been waiting for updates

hon hon hon both the suggest mangas in this little thread are brilliant :D and also hehe its brilliant though as its a name a 4 year old is actually likely to give a pet lol

Tensei Kyuuketsukisan wa Ohirune ga Shitai is also pretty terrible with names

Isn't that where the main character is split in two genders and he can also control his female counterpart?

Are you talking about this one?
http://www.mangago.zone/read-manga/the_rhapsody_of_me_and_her/
I don’t remember it well if he/she did tend to mess with people name though XD

Yep