If you're like me, your first response was probably, "Who goes around handing out pretzels?" The answer is, of course, pretzel vendors. Which means that President Kimball was simply giving a much-needed reiteration of the Biblical ban on prostitution.
Actually, I put some thought into this, and I believe President Kimball’s point was that pretzels are a trifling snack attributing no emotional significance. For example, suppose I had this bag of pretzels, which is nearly as endless as my capacity to kiss. Unscrupulously, I would gladly share this bag with anyone. Shucks, I’d share this bag of pretzels all evening with a stranger I fully intended to never see again. I believe this is the attitude President Kimball meant to discourage us from applying to kissing.