I'm not fresh from college, far from it, so my excuse is harder to sell though equally valid.
I tell them that I'm saving for a house (which is true) and that I'm actively looking (also true). I decided to stay at home longer because I have a great relationship with my parents (DHV) and my older cousins told me that they would do the same thing if they could go back in time (possible DHV).
Some won't bother when they find out you're living at home. Period. There's nothing you can do here but shrug it off and move on (to the next subject or the next target, take your pick). It's like women who won't give you the time of day because your not tall enough or have some other imperfection which disqualifies you.
Just make sure they know that: a) you won't be there for long (you're fresh out of college, so this is acceptable to most women your age), and b) you don't let the fact that you're living at home bother you.
I also throw in the fact that I have been free to come and go as I please since I was 18 (again, true) and that I live virtually rent-free, which has it's benefits.
The fact that I live at the opposite end of the house and have my own stairs is worth it's weight in gold. I can't tell you how many times I've had girls over and done the wild thing without anyone knowing... though I have had to cover a girls mouth a couple times because she was getting too noisy...