This is a topic I've thought a lot about recently. I posted a series of stories in the True Stories forum all centered around my wife being tickled by her female friend(s) and coworker and since doing so I've been trying to unpack it in my mind. There is something undeniably hot to me about watching my wife get tickled or even hearing her tell me about a time she was tickled when I wasn't there to witness it. I don't necessarily consider it cuckolding, but I'm not an expert and perhaps under some strict definition of the term it would fall under that umbrella.
From my perspective there's multiple aspects of a "someone else" scenario that turns me on and sometimes it varies based on who is doing the tickling. The first scenario that got me to post here recently was my wife Keri's coworker and friend Jenn tickling her feet for maybe 45 seconds after a work Christmas party. The first thing that comes to mind in this situation is the power dynamic. The two of them share an equal title at work, but Keri was responsible for training Jenn and she really took her under her wing. The two of them have become pretty close friends now, but there is a definite mentor/mentee thing at work. Then there is the personality differences between them. Keri is very "type A". At work especially, she presents as serious and has a real take-charge attitude. Jenn is bubbly, fun-loving and Keri always says that if she could, she'd spend all day at work chit-chatting. So to have witnessed Jenn tickle Keri was a display of flipping the relationship that they have built around a bit and it's also got a big element of Jenn figured out a "weakness" of Keri's. Something that can make her tough, no nonsense exterior crack a tiny bit. It's a trope, I know, but there's a reason why we like tropes I guess. That's why this situation above all others embarrassed Keri. I think Jenn taking such a step and catching her off guard was not something she anticipated. Furthermore, Jenn seems happy to now remind Keri of her ticklishness. Weeks later Jenn joked with another one of their coworkers about tickling Keri and her not being as tough as she seems, and it re-embarrassed her all over again.
On the other side of things is Keri's best friend Gianna. Gianna is a relatively frequent tickler to Keri. She's bigger than Keri and she's domineering and bossy in all aspects of her life. Contrary to the relationship between Keri and Jenn, Gianna knows the type of person Keri is, but they have a looser, more comfortable and honest relationship. Keri isn't up tight around Gianna at all. But the the main things that are a turn on about Gianna tickling her is that she uses it as a way to playfully bully Keri. She seems to enjoy tickling not as a fetishist but as someone who likes to exploit a "weakness". Gianna is just a tickler. Some people are. I've seen her tickle a lot of people over the years. There's something she enjoys about tickling another person, even if it's not at all sexual or fetishistic. She likes to tease Keri about her ticklishness and especially during the times she's tickled her. Gianna also is the only person aside from my wife (and maybe some of my exes) who knows about my foot fetish and she teases Keri and I about it quite frequently. Sometimes, I get mad, but Gianna and I are very close friends, so I never let it bother me that much. If I'm being honest, I do like the idea that she knows that she's driving me a little crazy when she tickles Keri's feet. That's very hot to me.
And then there's my wife's role in these situations. She never encourages it or seems to initiate a tickling, but she definitely doesn't go out of her way to guard against it. She's always barefoot. In fact we were just at Gianna's house last night and the first thing she did when we got there was take off her shoes. Gianna's house is a "shoes at the door" house, but Keri almost never wears socks there. My wife doesn't hate being tickled. I'm not sure she likes it, but she doesn't hate it. She's never been tied up and tickled seriously (it's not an interest of mine) or really experienced any kind of "tickle torture". When her friend(s) have tickled her, its always kind of playful. There's always some effort to hold her still but mostly, if she really wanted to get away she could. So for her, I don't think she's really ever thinking "i don't want Gianna to tickle me so I'll wear socks". I don't think it's a thought in her head until she's actually getting tickled. And the other aspect is that she knows I love it. She knows watching her get tickled, especially on her feet, drives me crazy. I think there is a part of her that likes that, but not enough to purposely try to get Gianna to tickle her.
So these situations that I've witness or the few that she's told me about have become a big part of my fetish. When we hang out with Gianna, I'm always hoping she'll tickle Keri. It's always in the back of my head now. But we see Gianna multiple times a week for the last 15 years, and she's only ever tickled Keri in earnest maybe 5 or 6 times (I'm not counting little things like quick rib tickles or a single quick graze of her foot), so the odd are not on my side. Jenn tickling her took me by complete surprise, which is why it was so incredible hot to me. I never thought in a million years she'd tickle her like that, but I almost expect it from Gianna.
As far as cuckolding though, I don't know. If a man were to tickle my wife, there'd be a problem. Nothing about that idea turns me on. I think a big part of why I like when a female friend has done it has to do with playfulness. It's almost that "girls at a sleepover" fantasy for me. Thinking about another man touching and tickling my wife in any way isn't the same. Interestingly, as a thought experiment, I thought about a lesbian tickling Keri and indicating that she was into it. That idea doesn't bother much. I've also considered the possibility that Gianna is actually turned on by tickling Keri. I don't think it's the case, but I mean you never know. Somewhat oddly, this doesn't bother me. Keri's joked with Gianna about her enjoying tickling her and in a private conversation with my wife I once said that I thought if enough wine was involved, Gianna would suck Keri's toes. I was only half-joking, and Keri wasn't amused, but if something like that were to happen while Gianna was tickling Keri, I'd be very turned on by that. I suppose that I know my wife isn't into women, so there's no real sexual threat there. It's complicated, I guess.