Basic Trope: Someone sends a mass, unwanted message (usually of commercial nature) to tons of e-mail addresses, posts it to fora, or uses other methods to send/post it. Alternately, someone posts something repetitive and of zero value to where it's posted.
Bob (or, more commonly, an automated program he's using to do it) sends ten million random people an advertisement or a link to malware.
Bob posts "First Post!" as a reply to anything and everything where he can get first post, and "Me Too!" when he can't.
Bob (and/or his bots) becomes notorious as the "Spam King" for unrelenting spamming of repeated communications outlets, clever evasion of anti-spam measures and laws, and actually making real-life money off of the spamming or virus infections.
Bob's entire life is consumed by his burning need for First Post and/or to make self-promotional or other meaningless or unwanted comments, on anything and everything.
Spam overwhelms a communication venue to such an extent that legitimate content, posts or comments are far outnumbered and eventually the legitimate posters leave in frustration, either with the spam or with the draconian anti-spam measures taken to stop it. (For example, the presence of CAPTCHA or RECAPTCHA in too many places tends to anger legitimate users even more than it deters spammers, who can break it if they are determined enough.)
Bob sends out the occasional "sponsored tweet" or other advertisement, and it may even be for something sketchy or crappy, but he also makes a fair amount of non-spam postings, enough that the spam is ignored.
Similarly, Bob occasionally forwards Urban Legends or promotional content, but not so much as to upset people or convince them to block or ban him.
Bob got hacked and The Cracker sent out spam. On finding out about the hack, he changed his passwords and posted proper apologies. No more spam ensued, so it was obvious he wasn't the Spammer.
Justified: A ha ha ha ha... NO! NEVER!
Bob is working in some sort of anti-spam capacity (anything from a forum moderator to corporate IT) and has to combat spammers and spam.
Bob sets up an anti-spam program to block spam or a honeypot to catch spammers.
Bob appears to be spamming, but is testing the anti-spam system.
Bob appears to be spamming but it is an April Fool's joke.
Bob takes control of a botnet to warn people not to open the spam it sent out and send out links to antivirus and anti-malware tools to undo the damage it caused.
Bob's post appears ten times, annoying everyone and making them think he's spamming it; when they see their own comment repeat as well, they know there's a server issue.
Bob is only testing the anti-spam system to figure out a better way to spam.
The April Fool's joke is itself spam.
The antivirus and antimalware tools offered in the botnet's new links are ransomware and scareware as opposed to being legitimate tools to fix its damage.
Parodied: "Scambaiting" where spammers and scammers are baited into believing they've found a mark, and "spoetry," poetry made from spam.
Someone posts in the moderator only forum on a popular forum declaring the ban of a spammer or warning about a new spam tactic.
Conversed: "Maybe we should have a movie centered around Bob the "Spam King." "I don't think anyone would want to see that unless it involved his Cruel and Unusual Death."
A letter or notice from an ISP mentioning violation of terms of service is shown.
[SPAM] [100,000 Unread]
Plotted A Good Waste:
Depicting someone as a Spammer so as to make them so entirely unsympathetic anything can happen to them and be funny or seen as deserved.
Depicting someone as the Spammer in an attempt to tell a story about how economic desperation drives people to criminality, including spamming, and to try to make even something most people have little to no sympathy for seem sympathetic.
Having some junk communications in any universe that features communications (from mail and phones to e-mail and fora to even cybernetics and telepathy) to add realism and verisimilitude: if there is a communication media in Real Life, it will have at least some problem with unsolicited and unwanted commercial communication.
Bob is banned from the communications venue and possibly his ISP.
Bob is arrested and tried for violating laws relating to his spamming.
No one likes spammers and all of the spam is deleted and ignored.
The spam actually does appeal to enough people to make it worth the cost of all the people enraged by it, at least monetarily.
Bob becomes a trusted figure among spammers for knowing how to spam and get away with it.