Kaspar Hauser.
Underhill
Charles Carmichael
Si
I’ve used the name Jimmy Reilly or James O’Reilly before. Was the protagonist of a book I read a million years ago.
If I were a guy, I would totally use Heywood Jablome. Phil McCracken is a good second choice, though.
Awesome. Mr. Underhill from the Shire I presume?
See also “Pat McGroin.”
I want to change mine. I plan to use Ray P. DeKlaun from this point forward.
Mrs. Congeniality.
Clyde. First or last name, depending on where I am.
I’ve also used “Donner” as a name to give the hostess at a restaurant. Only once did someone get it and play along. We were told our table was ready with the call “Donner, party of 8. Correction, party of 5.” 
Will DiCoca.
At your service
Dante Jacuzzi.
If anyone questions it, I add that my grandfather invented the Jacuzzi.
Max Power.
I got it from a hair dryer.
Actually, no it’s never come u-- waitaminute, yes it has. I signed up for classmates dot com at my wife’s high school so I could look up some of her classmates for her, and I chose John Smith.
I usually use the name of the place I’m at. e.g. if I’m at Starbucks and someone asks my name to call my order, then my name would be either Star or Buck. If I’m at Maggianos, Maggie. If I’m at Wendy’s, then I’d be Wendy. etc… Of course most fast food places go by number nowadays when they call you.
If I’m at a hotel, I always pay by credit card so I can’t make up a name.
I’ve used Richard Starky and Robert Zimmerman before. Kinda crappy pseudonyms since probably a non-trivial number of people would recognize the names, but then I’m not usually using a fake name for any reason other then to avoid a minor annoyance, like avoiding junk mail or pranks. When I become a international man of mystery, I’ll have to come up with some better ones.
H. E. Pennypacker
or
Dr. Martin van Nostrand