Backtagging: Absolutely. My job sometimes slows me down a bit, so no problems with this at all.
Threadjacking: I'm all for it, as long as it doesn't turn into a case where two other characters tag for an obscenely long chain of comments and/or lock Rex out of it. If it looks like the thread is going to run more than 20-25 tags between both characters, I'd appreciate the conversation being taken to a new post where the other two characters can continue their conversation.
Fourthwalling: If any other characters did actually know anything about Rex and his canon... For the most part, HELL YES. This is an opportunity for confusion, embarrassment and hilarity. The only time I would like to discuss this first is if it involves something crucial to Rex's lost memories. Otherwise, go for it!
Offensive subjects: I have yet to really run into problems with offensive material, but if you're not sure, check in with me.
NAUTILUS CITY SHIFTS AND GIFTS: If you want to request something major in my stead, such a physical alterations (Rex turning into an animal for example), please ask me first. If you are requesting something minor, such a gifts of clothing, toys, other items, please alert me to the request on SotG so I can 1) be aware of it and 2) agree to or turn it down. If I request something myself, I obviously want it and will receive a notif if it's approved. There have been instances in the past where other players have requested things for my characters, however, and they were things I didn't want or didn't find out about until much later. (And you will know if I found out on my own because I will comment to you on the SotG. If no comment ever comes, I'm oblivious to the request.)
Casual Contact: Pats on the back, hand on the shoulder, it's all fine.
Hugging: Oh my god everyone ever hugs this kid in canon. He's used to it. Though if he doesn't like the character doing the hugging, he'll probably push them away.
Kissing: Sure! Reactions will vary depending on what he thinks of the character doing the kissing, of course. At worst, they'll get shoved. At best, he'll kiss back. XD
Flirting: Feel free. He's something of a
terrible flirt, himself.
Fighting: Rex loves to fight, so yes. Just be warned that he's quite tough and has one hell of a bag of tricks. (See the next two parts for further information.)
Causing Injury: Yes, to an extent. I'm okay with him being knocked around, thrown into/through walls, bruised, cut and stabbed. His machines may also be smashed/destroyed if hit with enough force. For anything really gory like loss of his real limbs or other types of nasty disfigurement, check in with me first.
Killing: No. Please discuss this with me well in advance (especially since Rex is about as easy to kill as a damn cockroach).
Mind Reading: He's definitely readable. I do want to have a say on what's there to read in any given log/thread, however, mostly so the wrong info doesn't end up out in the open before I'm ready for it to be there. (Also keep in mind that some of what's in Rex's head is not openly accessible even to him.)
Stealing Items or Data/Pulling Pranks: For stealing, check in with me so we can discuss what belongings are okay to swipe. I'm all for pranks, however! Rex is a something of a prankster, though, so be aware that revenge may be forthcoming. ;)