Friendship is like peeing on yourself: everyone can see it, but only you get the warm feeling that it brings.

The line is a deliberately crude, comic simile that treats “friendship” as something publicly visible in its outward signs (people can tell you have it) while its most important payoff is private and subjective (the “warm feeling” only the participant experiences). The joke hinges on incongruity: friendship is conventionally ennobling, while the bodily image is embarrassing, so the comparison punctures sentimentality and replaces it with sardonic realism. Read more charitably, it suggests that the value of friendship is primarily internal—felt as comfort, reassurance, and belonging—rather than something to be performed for social approval.