My '77 Husqvarna WR250 - Old Satan. Because it temps me to do BAD things that will not end well for me.
'92 Ex500 - Michelle. After an old girlfriend. Because I never knew if she would break my heart or break my arm, but she sure was pretty to look at and fun to ride!
'86 Honda XL250 - Thumper. Of course.
'08 KLR - Tiller. Because if I'm not careful it makes the yard look like I've been through it with a roto-tiller.
'89 Chevy C1500 - Old Faithful. It doesn't break. Ever.
'91 Geo Metro - Dick Turpin. Because it's always holding people up on the highway.
Last but not least, my '01 Polaris trailblazer - usually just call it START, DAMMIT. The only part of this AMERICAN atv that I've ever had problems with is the JAPANESE engine.