Given that these glyphs were developed thousands of years ago by former cave dwellers who were unconstrained by religious taboos, and were rather intelligent, it is only natural that the sages used the single most pleasurable of human experiences known, that of orgasms and oral sex, to describe JOY, PLEASURE, ENJOY, GRATIFICATION mutually between two or more parties. Stated another way, it would have been rather unnatural for a glyph meaning PLEASURE and what is LIKED not to reference sex directly (by instead depicting joy using elements of drum beats or foot washing or warriors eating beans, as some have suggested). Glyph plainly describes early fundamentals of how to win friends and influence people.
Merged elements of「penis」and「clitoris」as an action which itself often produces MUTUAL GRATIFICATION. Or,「spurting stance getting lucky with orifice, mouth.」Formerly referring to「erectile tissue in an orifice」being PLEASING, a reference to mutual oral activity of all varieties:「Oral sex is good for women's health [and men's, too, it would follow] and makes you feel happier, according to a study which studied the effects of semen's 'mood-altering chemicals.' The State University of New York study…follows research which shows that seminal fluid contains chemicals that elevate mood, increase affection, induce sleep and also contain at least three anti-depressants. …Semen contains [other] chemicals along with spermatozoa, including cortisol, which is known to increase affection, estrone, which elevates mood and oxytocin, which also elevates mood. It also contains thyrotropin-releasing hormone (another antidepressant), melatonin (a sleep-inducing agent), and even serotonin (perhaps the best-known antidepressant neurotransmitter).」
[ https://www.dailymail.co.uk/health/article-2190863/Semen-good-womens-health-helps-fight-depression.html 2013-01-20 ]
Given the predominant use of the Internet, many forms of entertainment, and just the plain old free time of most humans today, it seems as a species that we humans have not changed much in the past few millennia, and that sex, especially oral sex, is still one of humanity's greatest pleasures (no suggestion is implied that we should have changed, either). The first Western scholars in Asia were religious missionaries, priests, or monks who were constrained from telling the truth about sexually explicit glyphs, and so these old religious men said that the elements were: a hand with pot on one-legged stand used as a bongo drum…. For obvious reasons, two of this glyph repeated side-by-side (囍) means「happily married couple」and not percussionist duo.

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: to be fond of; to like; to enjoy; to be happy; to feel pleased; happiness; delight; glad
Japanese EDRDG: rejoice, take pleasure in
Unihan extended: like, love, enjoy; joyful thing

Used within names (nanori)
あき　･　きゅ　･　のぶ　･　ゆき　･　よし