I recently watched The Perfect Husband (as part of my ongoing Tim Roth infatuation) and had some thoughts about different types of "Ladies' Men." The words below (Don Juan, Lothario, Casanova) are usually used as rough synonyms, but in my research I discovered entirely different emotional tones:
The Don Juan (or Lothario, if you prefer), is a serial womanizer - his career is built on a pattern of taking advantage of women's affections, generally leaving them in the lurch when the inevitable yearning for the next conquest begins. The Don Juan's focus is fundamentally on the use of (large numbers of) sexual conquests to prove his own masculinity and success as a man. (He's well-acquainted with a relentless internal monologue on the topic of his own inferiority as a man; more often than not, this inner voice is the voice of his father.) His lovers often live to regret their dalliances with him, particularly as Don Juans are master manipulators of feminine emotions and inclined to be irresponsible about such matters as discretion and birth control.
The Casanova is no seeker of self-aggrandizement; his goal is simply (and magnificently) 'salvation through love.' He genuinely loves women and enjoys their company; each of his affairs (and he has many - some brief, some extended, very often concurrent) is truly a love affair. Nevertheless, since no woman can replace her whose love really is capable of granting salvation - his mother, either in warm childhood memories or in wistful childhood imagination - each affair ends in its time, usually with care taken to minimize harm (emotional or social) to the woman. Casanova's affairs are subject to recurrence years or decades later, because he leaves behind him a warm affection that is easily rekindled.
A Don Juan is preoccupied with his own manliness, so is prone to other manly excesses such as fighting, over-indulging in drink, etc. A Casanova prefers the company of women, since men have nothing to offer him in his quest, so eschews many traditional strongholds of masculinity; hunting and brawling have little appeal. In fact, the sexual orientation of a Casanova may, from time to time, be called into question for this reason.
For a Don Juan, sexual pleasure is of secondary concern, and is liable to get lost in the need to demonstrate sexual prowess; he's likely to be an aggressive and persistent (but not especially skilled or subtle) lover. A Casanova views sex as an expression of the (often short-term but still real) love between the parties, and is also likely to have made love with any number of older women in his youth; he's usually a skilled and sensitive lover, knowledgeable in the ways of pleasuring a woman.
Given his obsession with his own status, a Don Juan tends to pursue young women of great beauty, high social status, etc. ; naturally these affairs must become known by at least some, in order to serve their purpose as marks on the Don Juan's personal scorecard. A Casanova is minimally interested in social perceptions of his affairs, and indeed tends to be quite discreet; his lovers may vary considerably in age, personal beauty and social standing.
Anyone care to suggest some further distinctions or subtypes?