Others aren't necessarily interested in the penis, but in what it can tell them about the man it belongs to, how it signals his erotic desire.
People often engage in "oral sex," using their mouth to manipulate the penis and bring the man to orgasm, usually swallowing his semen at the end.
Oral sex can have a utilitarian function, to express affection and establish emotional intimacy in a relationship, but most often it is recreational.
In fact, it is probably the most common form of recreation in gay communities.
Oral sex is rarely a stand-alone activity. It usually happens in conjunction with other recreational activities:
The dinner and a movie of a date
The conversation and games of a party
The workout and sauna of a bathhouse.
This is a slice of pizza, a dish of cheese and various meats and vegetables with tomato sauce on a thin crust.
Although it has some nutritional value, and can be used for utilitarian purposes, it typically contains 600 calories, 32 grams of fat, and 1300 mg of sodium, more than what you want for dinner.
Therefore it is most commonly consumed as a form of recreation.
Like oral sex, eating pizza is rarely a stand-alone activity. Most commonly it accompanies other forms of recreation:
The movie and sex of a date
The conversation and sex of a party
It is often served at bathhouses on "Pizza Tuesdays."
Eating a slice of pizza and going down on a guy's penis have a lot in common:
1. They require your mouth.
2. They both end with something in your stomach.
3. They are both primarily recreational rather than utilitarian.
4. Both usually occur in conjunction with other recreational activities.
5. Usually in a group.
6. You can do both in bed.
7. It is quite likely that you will do both on the same evening.
But they have some significant differences.
Pizza is about the food instinct, centered on the sense of taste. What the pizza feels like in your mouth is irrelevant. Therefore a slice of pizza is never erotic, sexy, or attractive.
The penis is about erotic arousal, centered on the sense of touch. What the penis tastes like in your mouth is irrelevant. Therefore a penis -- and the guy it belongs to -- is never tasty, delicious, scrumptious, mouth-watering, finger-licking good, delectable, nom-nom, or yummy.
Using the inappropriate terms, or otherwise treating food as a sex partner or a sex partner as food, is disgusting.
Never use a taste-term to describe a man or his penis.
Never lick any part of the body except the penis and testicles.
Never consume any fluid that is pooled outside his body.
If you do, I'll kick you out of bed. I don't care if you're Nolan Gould, and you offered to buy pizza later.
See also: What Not to Say During Sex; The Most Disgusting Hookup of All Time.