I would expect it to have happened in the ‘old days’ when there were only 16 teams or less. Recently we had euro 2008 which had a group with WC 2006 finalists France and Italy. The group was eventually won by the Netherlands (talking about group of death!) after beating both by three goals. Not exactly what you asked for… but ahh, the memories ;).
These would be the toughest draws IMO:
Brazil, Mexico (or USA), France, Holland
Brazil, Mexico (or USA), France, Italy
Germany, Mexico (or USA), France, Holland
Germany, Mexico (or USA), France, Italy
I thought I’d have a look:
1934 - no groups and defending champs Uruguay didn’t travel to Europe.
1938 - no groups
1950 - Groups but losing finalist Czechslovakia didn’t play. No final per se but the last game in the winning group round between Uruguay and Brazil decided the winner.
1954 - Groups with Brazil and Uruguay drawn in different groups.
1958 - Groups but Hungary and West Germany in separate groups.
1962 - Groups but losing finalist from 1958 Sweden wasn’t there.
1966 - Same as 1962 - losing finalist Czechoslovakia didn’t attend.
1970 - West Germany and England in separate groups
1974 - Brazil and Italy in separate groups.
1978 - Netherlands and West Germany in separate groups.
1982 - Netherlands failed to qualify
1986 - Italy and West Germany in separate groups
1990 - West Germany and Argentina in separate groups
1994 - West Germany and Argentina in separate groups
1998 - Brazil and Italy in separate groups
2002 - France and Brazil in separate groups
2006 - Germany and Brazil in separate groups
2010 - Italy and France in separate groups.
I really hope it happens just for giggles.
Holland, Italy, Mexico & the USA are all strong candidates to be in a “Group of Death”. Maybe Japan too. That’s assuming the teams are sorted into the pots the way they’ve historically been. Which sucks since I’m a huge fan of two of those teams.
I think it’s a safe bet that the format of the draw won’t allow there to be more than two UEFA teams per group ruling out the last two possibilties
If we assume the likely format is:
Pot 1: seeds, Pot 2: unseeded UEFA, Pot 3/Pot 3 + ‘special’ Pot: CAF, unseeded CONMEBOL + France (as lowest ranked UEFA team), Pot 4: AFC and CONCACAF,
For the toughest possible group I’d take Brazil from pot 1 as it would be almost inconceivable for them to go out in the 1st round on their home turf and also as a non-UEFA team it allows France to be in the group. Italy from pot 2 as again they’re very unlikely to slip up in the 1st round. France from Pot 3, though Chile would also be a tough team. USA from Pot 4 or maybe Japan (I wouldn’t Mexico though as they are a complete shambles at the moment).
Another draw simulator. This is one is more elaborate:
Hey, I’ll take that! My draw came out with the US finishing 2nd in Group D behind Uruguay, but beating out Russia and Cote d’Ivoire.
2nd round - victory over South Korea.
3rd round - at long last we beat Ghana!
Semis – the US takes down Argentina!! We’re into the Finals!
Finals – lose to Colombia. Damn it Klinsmann! Why switch to a 3-6-1 before the Finals, WHY?!?
This draw also has Brazil finishing last in Group A behind Ghana, England and Japan. Hmmm… sure, why not?
I guess the newly-announced twist to the draw means that some pretty horrendous groups of death are now possible. Apparently one team will be randomly chosen from the nine-team European pot 4 and put into pot 2, with the constraint that they can only be drawn into a non-European seed’s group. That means that groups such as Brazil, Italy, USA, Netherlands are possible, if unlikely.
Man, this is getting confusing 
Welcome to FIFA?
FIFA, where you just need to leave a brown envelope at the door to get things done
And the draw begins.
The U.S. is so f**ked. Germany, Ghana, and to cap it off, Portugal. Great.
Edit: So, with the gigantic grain of salt that FIFA rankingsshould be taken with, that’s the 2nd, 5th, and 24th ranked teams along with the 14th ranked U.S.
Tough group for the USA.
Group A - Brazil Croatia Mexico Cameroon
Brazil, and who else?
Group B - Spain Holland Australia Chile
Holland and Spain go on
Group C - Colombia Japan Greece Ivory Coast
Seems like a really well-balanced group, any of the four has a shot.
Group D - Uruguay Costa Rica Italy England
That’s a tough one to be in - Any two of England, Italy, and Uruguay might go to next round. Probably not England though.
Group E - France Switzerland Honduras Ecuador
Fuck Platini and his manila envelopes
Group F - Argentina Iran Nigeria Bosnia
Interesting group, I’m glad for the Bosnians, looks like they have a shot at going forward.
Group G - Portugal Germany Ghana US
Sucks for the US, this is probably the ‘group of death’ for them. Bummer.
Group H - Russia Belgium South Korea and Algeria
This group is not really World Cup worthy 
Definitely the easiest of the eight.
I’d say E is the easiest and G is definitely the Group of Death.
Yep. Saw the draw and though, oh crap, we’re done.
I’ll say D is the group of Death, 3 former champions.
US can get through with 4 points and luck with the other results.
Fuuuuck though, really rough draw.
I’m not sure what wins almost 40 years ago for England and 60 fpr Uruguay have to do with anything.