On large car rims it is the portion of the inside of the wheel that is painted usually to match the cars paint job.

Red, engorged dog's penis

It is used as slang for a hot lesbian. The plural form being "lipsticks".

the pink tip that exposes itself from a male dog's penile cover when said animal is sexually aroused.

a lesbian that's very feminine, the exact opposite of a butch.

When a male dog becomes aroused and "unsheaths it's sword" resembling an extending lipstick.

a.) a cosmetic applied to the lips of a female; usually. Its use was developed in ancient times by prostitutes as form of advertisement, by painting their lips to match the same color as the inner folds of their vagina, so the male customer would get a glimpse of what he was getting. Lipstick was, then, various shades of red and pink. I doubt, if the colors were available, that any prostitute then would have painted their lips brown, black or green, which may have led the customer to believe that she may have a disease.
b.) Also refers to the male cock, whereas the cock being the stick that is placed between the lips; thus a lip-stick. Derived from the possible coating of the lips with sperm during oral sex as the male cock was brushed across the lips. This more than likely led to the development of the lip stick container; shaped much like the male cock, which the female brushes across her lips to apply it.
c.) Sexual slang for oral sex, as in “sticking”(the cock being used as the stick)fucking the lips; also know as “face fucking”, and “head banging”.