Throughout the story, Luffy often calls other characters not by their name. He tends to call them by his made-up nickname or just call them with shortened name.
For some reason it’s surprising to see how Luffy calls Pekoms as Pekomamushi. Prior to arriving in Totto Land, Luffy tended to say Pekoms’ name wrong, calling him Pekomamushi, possibly due to Nekomamushi’s similar sounding name.
Here are 20 memes about how Luffy calls the other characters: