I am just chiming in to say how cool it is that there are so many people passing on the CORRECT information about HSV and VZV (varicella/chickenpox/zoster) infections.
A couple of further points: It is always possible to pass HSV because carriers can shed virus even when there is no lesion. It's far MORE likely when there is a lesion, of course, but it is never completely impossible to pass it on. What the previous posters have stated about the large majority of the adult population being latently infected with at least one of the various strains is absolutely correct as well, and many of them do not know it. When we educate people about HSV, it's very important that we emphasize that no one may be "lying" about being infected--they may very honestly not know. Not everyone has even an initial full-blown outbreak.
HSV is also different from most other things that can be grouped with the STIs in that the virus is shed over a larger area. You don't have to touch the lips or the genital area. The description we usually use for genital herpes is the area that would be covered by swim trunks or boy shorts.
Finally, the VZV vaccine is a weakened live virus, so it is possible to get a (usually mild) case of chicken pox from the vaccine, and it is also possible to get shingles afterwards from it (both are documented). It is also possible to get wild-type chicken pox after being vaccinated, although again, usually it will be a much milder case. It is also possible for someone exposed to a recent vaccinee to "catch" chicken pox from them (this is why we don't give this vaccine to immunosuppressed people or to people in those households).
Canker sores are different from cold sores to a doctor--they are what we call "aphthous ulcers" technically--and they occur inside the mouth rather than on the lips or other areas, but the terms are often used interchangably by the public.