For me, it's more so when they go 'Thanks for favoriting LINKHERE' like... if someone really likes your work like 'Oh my gosh, I feel really honored that you favorited LINKHERE, I was worried that the shading was really off and since you got really nice shading, could ya give me some tips?' then it's a lot more okay imo, or if, as you've stated, brought into being a conversation starter like 'Hey, I saw you favorite my art and I'd like to thank you for that, though since it's X Files themed I'll take it you like the X-Files? How far have you gotten into the show?' then that's also alright.
Just the copy paste ones, especially with links bug me.