I do not recommend using the phrase, “I like you as much as I like this pen” to anyone. Although it could mean you like someone as much as your very favorite pen, it doesn’t come across that way after the first take. It sounds like the person you are referring to is being compared to a pen, even though that is not really the case at all. In reality the comparison is in your inclination towards the pen and the person being on par. Admittedly this is not the best way to express affection towards someone, it is better than saying, “you are like this pen.”
I did actually use this phrase. Thankfully my audience was understanding enough to realize I was in a somewhat estranged mental state and merely formulated a sentence that included the subjects before me and my feelings towards them.
Spots of Time 