Television crossovers that can only end in fisticuffs.

“Dull sublunary lovers’ love (whose soul is sense) cannot admit absence, because that doth remove that which elemented it.”

Kirk & Spock are not sublunary.

This is true.

That would probably be batleths first, bunk later. Jayne would spend the rest of the series making comments about Tom Paris having trouble satisfying a human female, let alone a half-Klingon.
How about Mos from IT Crowd vs McGee from NCIS. All of a sudden McGee would realise he is too nerdy to be a “real” field agent in the others eyes, but not nerdy enough compared to Mos. Mos of course would be Abbie’s new pet project. I could even imagine one of those black&white photo-flashes showing Mos in bed with Abbie and Ziva (if either are still in it - it’s been a while).

Yeah, I think we’re ignoring some of the necessary plot elements of both shows. Mal would be far too tricksy to get involved in a one-on-one fight either with the entire crew or involved in a space battle with Voyager. Rather, he’d do something sneaky that wouldn’t quite work out the way he’d hoped.

So, taking Voyager’s plots into account, this would mean that Mal and crew would suddenly find themselves accidentally in full control of the Voyager and crew (something that Janeway seems to have experienced no less than every third episode). Of course, Tuvak and Neelix, or Tom and Torres, would do some figuring and plotting, and regain control.

All of which would turn out to be according to the plan that Zoe and the crew come up with to get Mal out of the mess he’s made of things. Firefly and Voyager part ways, more or less unscathed. The crew of Voyager would have learned some basic moral lesson, and Firefly would have a hold full of Starfleet goodies - valuable, but not so valuable that they can stop worrying about money for long…

Mal: You took a what, Kaylee?
Kaylee: It’s a Replicator, Captain. It makes all kinds of food and beverages.
Jayne: Does it make beer?
Kaylee: Not so you’d call it such.
Jayne: Then what good is it?
Mal: A regular full belly is good. Good job, Kaylee.

How about Murphy Brown?

“How I Met Your Mother” meets “Buffy” - Barney takes Willow to be a younger doppleganger of Lily (in the HIMYM universe, non-evil dopplegangers are reasonably common) and attempts all sorts of seduction ploys. This ends poorly for him. Ted annoys Spike (automatically), which also ends poorly for Ted. Marshall however gets along with just about everybody (although he recognizes Willow’s resemblance to Lily, he’s thoroughly fixated on Lily, so no problems occur).

Now when Agent Mulder starts asking nosy questions in Mayberry, he’s bound to be punched out by someone (if not Andy, then certainly the Darling family)…

Especially if Vamp Willow and Dark Willow show up…

Yes, I guess so. More or less. You had to go back fifteen years, though (!)

I was going to suggest Maude, which requires going back even further.

Don’t know about that but I’d pay to see Voyager with Al Swearengen in the captain’s seat.

Going way back, the magical cat fight between Jeannie and Samantha Stevens, prompted when Endora makes a Darren look like Major Nelson.

Jack Bauer and Batman (the Adam West version)

Jack: The Riddler is a known terrorist in league with Abdulla Ghoti, code named “fish”. He’s spelled out his plans in the marinara sauce.
Robin: Batman, look! What skinny macaroni!
Batman: No, it’s spaghetti, Robin. A variety of alimentary paste, larger then bernachelli but not as tubular as macaroni.
Robin: Ghoti is fish?
Batman: English phonetics, Boy Wonder. GH becomes F, as in tough or laugh. O becomes I as in women. TI becomes SH as in ration or the word nation.
Jack: With all due respect, sir. Every second we waste increases the search grid along with his chances to escape.
Robin: The Riddler won’t get away from Batman that easy!
Batman: Easily.
Robin: Easily?
Batman: Good grammar is essential, Robin.
Robin: Thank you.
Batman: You’re welcome.
Jack: That’s it! (violence ensues)

Hey. Don Draper and Darren Stephens are contemporaries in the same field - what would Samantha think of Don? Or, say, Uncle Arthur…

Speaking of Mayberry, I’m sure Sheriff Taylor alone would drive Gibbs to fits, let alone Barney Fife and the entire rest of the town.

More slash, eh? (Can’t see Uncle Arthur being inspired by Don to fisticuffs.)

If Don was offensive towards Samantha or towards Arthur himself, Arthur might throw a punch (not very well, I’ll admit).

Or Maude vs Livia Soprano?

Pair up any show with Route 66…Buz Murdock will end up fighting somebody.

I was thinking about this one the other day, as I watched the two shows on, um, Me TV I think. Jeannie’s a lot more powerful than Samantha (and less dependent on spoken spells), but Sam’s a lot smarter. Sam gets her ass kicked in the first fight, but assuming she survives she owns Jeannie in the remmatch.

There is, incidentally, no version of this tale in which Dr. Bellow survives.