A trundle is someone who you adore beyond belief (a best friend/family member) who happens to offend you greatly without meaning to do so. Someone who you want to wound without causing permanent damage.
-Hey Kat, don't you have mono? Or was it HiV?
-What?whatwhatwhat GABIE YOU TRUNDLE
-AHHHH! I'M SO WOUNDED!!!
-But not permanently.
-Oh. You're right. Cool. Sorry.