Anime initially was a guilty pleasure (at least, admitting watching it), but I think more related to it still, is watching more mature anime that borders ecchi or yuri themes/undertones. On the bright side, I can at least pass off alot of things I do, guilty pleasure or otherwise, as a way to fight off boredom. Initially, I started watching anime after running out of shows (especially sci-fi themed) to watch. Fortunately, I learned of Trigun beforehand thanks to a class outcast bringing it to pass time in a class (showing something to pass no-work-left classtime). It interested me, but it wasn't until I watched Lupin III that I really got hooked, and then I gave Inuyasha a shot, and got hooked on anime since then. At least nowadays, if anyone in my family takes interest in shows, I'll at least pick out ones with as little fanservice as possible to start, then work on from there. I mean, I don't want the fanservice to be everyone elses' reason for why I watch a particular show. It happened before with LEXX, and that was a live-action TV show on Sci-Fi (Damn you 4th season!!!); apparently the 4th season was riddled with fanservice.
As for less silly (though not less of a) guilty pleasure, I would say cursing in anger or intentionally for personally-observed comedy (or basically, what I would find funny/entertaining) that makes such good use of cursing that it's a bull's-eye precision F strike. Reason cursing is a guilty pleasure for me is because I was essentially "the good kid" for a majority of my life, and the only times I cursed was by accident, or not initially knowing what the curse meant. Nowadays, I can easily hold on my own without cursing, and I'm proud of that, but letting off an F-bomb here and there at the right moments is rather relieving. Unusually though (back in the days of my social networking), I cursed near-regularly in some of my posts and updates, but it just doesn't hold the same appeal as speaking my mind uncensored. Problem with the actual vocally cursing, I am too polite to do it in front of people, but privately, I can make the most hardened person blush.
I suppose a perk for not cursing for so long in my life was that my wit gets sharper than a razor's edge and without having to resort to vulgarity in order to outwit someone. It's even more fun and funny if someone is cursing like mad at me, or there's an opportunity to snark or something like that, I just whip out a witty statement and outclass anyone that would have to resort to cursing to match my level of wits. At least that's sorta rewarding on it's own. And even so, if I were to resort to having to curse, it would just enhance my wit if used properly.
I think one other guilty pleasure I have is relaxing my mind enough to the point of turning into a total nutjob. But to put it in a way less disturbing, I let my inner-child take over for a moment. It is surprisingly relaxing, and most the time, I would resort to doing something nostalgic anyway, usually something involving old games or letting my imagination run wild. Don't worry, I do have limits to at least keep myself remotely normal to the common person. I know how I look when I do that, but it does make coming up with ideas and such much easier. Also coming up with ideas feels less like work, and more like play. I think I made what would seem like an entire universe made of my ideas, and somehow, it all worked perfectly. Total melting pot of ideas working with each other like a massive Rube Goldberg device in perpetual motion.
Sorta related to that, if my computer and TV aren't enough, I still use my environment (like using my desktop setup as a military base), toy cars and stuff that look like they would be ships and such, and if need be, my hands, to make my own little battle scenes and such, and play (or continue) a game I have running in my head. It's a shame I can't upload the kind of things I come up with and make it distributable. I mean, one little fantasy/Sci-Fi campaign I made up in the pocket-verse game, I managed to turn a mage's staff into a magic shotgun, and I use it to obliterate tanks, and fire lightning bolts as fighter jets and such. And in more RTS game-like setting I run in my head, I prove to myself time after time just how badass some of my designs are. I even used Bloodfist in a campaign, and it mopped the floor with a small army by scraping the ground with the bottom of it, clear-cutting the troops in a line, and the crossbowdwarves got the stragglers, while the ship was also sling-shooting itself around a bend taking advantage of the ballistae grappling hooks to swing around. Hearing the noises my mind comes up with these sort of things also makes me wish I could just download some of my thoughts on a machine more.
I guess to summarize all that, my true guilty pleasure is that I'm still a child at heart. I mean, I'm still the mature one when I need to be, but I still have childlike tendencies one time or another; at least when it wouldn't get in the way. It does make hanging out with my nieces and nephew a bit easier to do. Fortunately, my nephew has gotten me to play some classics one time or another again; at least with some games I wish I had a second player to join me in.