The RS232 voltage spec:
-3V to -25V = logic 1
+3V to +25V = logic 0


However, if you take a look at a lot of the "MAX232" class chips you'll find that the RXD receiver input has the following characteristics:
Input high threshold: 1.7V (typ), 2.4V (max)
Input low threshold: 0.8V (min), 1.8V (typ)
Input resistance: 3K-7K ohms (pull-down to ground)

Those levels are actually close to what you'd get out of most TTL outputs! It's not "RS232", but you can pretty much drive that directly from a PIC output pin.
I wouldn't do it for a real commercial product, but for a one-of you could probably get away with it.

Connecting to the TXD level from an RS232 output is a different story. There you have to deal with the fact that you might get as much as +/-25V levels on the pin.