Luffy only bothers to remember the names of people who have earned his trust and/or respect. Although I’ve noticed he refers to Blackbeard and the Navy Admirals by their titles/aliases which likely indicates he recognises them as dangerous adversaries. The only enemy I’ve seen Luffy refer to by name is Kaido. Funny given how he has silly nicknames for many of the other Beast Pirates based on how they look or him mishearing their names. I actually chuckled when Luffy referred to Holed’em as Boldama and he responds with “who is that?!” Also funny how he refers to Queen as Balloon and Speed as Horsey (which likely inspired Otama to give Speed the name Horsalina)
