- Messages that are too short. E.g. "hey babe" doesn't mean much, when a women gets 10 - 20 "hey babe" messages in a day.
- There are men that get frustrated at the lack of response from women, and start turning their messages into "form letters" which don't show any level of having read the woman's profile.
- Initiating conversation with sexual propositions.
- Depending on the platform, sending unsolicited pictures of genitalia.
While some of these might not qualify as "spam" compared to a 419 scammers emails, I would say that wading through all of that seems akin to wading through one's spam folder...