The Weather Aboveground
When conversing with co-workers, there really are only two topics of ultimate inoffensiveness: the weather and the weekend. The weather is always safe, and you can even reveal a comfortable amount of roguishness by saying that you "really like" the rain or don't mind a sudden mid-summer temperature drop. This shows that you're a rebel, but a safe one.
Asking and answering questions about weekend plans is also fair game, unless your weekend plans have to do with snorting blow at the Gypsy Tea Lounge or getting a handjob in the backseat of a cab.