omggg. i think they like to talk nasty generally but nastiest.... i think its the breeding kink 😭 i MAYYY be biased. also, somehow it is more nasty (/pos) when they are in bodies where impregnation is not possible. like "oh you're so crazy about me you will break reality itself to leave me with child????? you're going to fertilize my non-existent eggs?? wowwww 😫" so charles begging erik to get him pregnant or knock him up, not to pull out, to keep his cum inside him "so it takes", erik telling him he looks fertile or saying he's going to fill him with his seed

specifically for 616, i also think the unabashed way erik talks about charles' body really turns him on, as someone who is more reserved and has spent so much time within a respectable persona. talking about his fat ass and his fat nipples or telling him he looks fertile and breedable...how he just wants to sink his teeth into his ass, lick him from hole to balls....it makes charles blush, and it also makes him dribble pre uncontrollably 🥰

i also think 616 charles has a bit of a humiliation kink and enjoys being called a slut. though, im not sure they'd use those words too often bc they're old — so words like "whore", "tart", "slag", "minx". always lovingly, teasingly, a little something to make charles moan, unless they're doing a whole bdsm scene about it