This is hilarious! I have annoying people like this in my department as well. I’m glad you are having fun with it. You have to update us!
One I love is everyones need to use the phrase “Let me know” at the end of every email. Like if you didnt add that in there I wouldnt answer the questions you previously stated in the email. “Well, he didnt say to ‘Let Him Know’ so i’ll just go ahead and delete this…”
He hasn’t responded. 
He sent me an e-mail about something else, but made no mention of the FYI thing. My thought is he saw it and was like, “What the hell is this?” and deleted it. Strangely enough, this mirrors my response to half of the e-mails I get from him. I’m going to keep doing it until one day he asks me what the hell I’m doing.
Little do you know, he’s a member of these boards. You can expect a new thread within a few days complaining about an employee who keeps forwarding him things. 
My boss does this, except she says “Please handle.” And she deletes from the communal e-mail while I was in the process of handling it so she can send it to my private e-mail so I have to find my place and start from the beginning. Sometimes I answer “That is what I was doing,” but she never replies.
Time to step it up. Instead of forwarding emails, just send a brand new one to him with nothing in the title except “FYI” and nothing in the message except “FYI”.
I wonder if he automatically forwards email to other people as well? It would be interesting if he were to get an official-sounding fake email, just to see who he forwards it to. You know, maybe adding a random sentence into some boring pronouncement that says “and furthermore, Casual Friday has been replaced with Clown Shoe Thursday, effective immediately.”
I’d just reply to every single FYI he sends you, changing the subject to “Noted”.
Or respond IYF. Because the e-mails bounced. In Your Face.
This is perfect! So if he asks “Why are you sending me e-mails with absolutely no information?” I could say “For the same reason I’ve always assumed you did: it makes me feel on top of things.”
FYI, I’m subscribing to this thread to see what happens.
FYI.
See, for all of you with elaborate schemes to respond to your clueless e-mailers with silliness, I’m thinking they’re too clueless to ever get what you’re doing. And then you’re just wasting your own time and brains with the silly responses.
I don’t have a problem with being forwarded useless information, thank goodness. What I do have to deal with are e-mail responses that read as if the recipient didn’t quite understand what I was asking for, and then we have to go around in circles a few times with what should be a very simple issue.
Years ago we did have an Associate Director (the second-in-command) who was a very nice lady but a little clueless. She regularly sent everyone charity-type glurge e-mails, like “do this to raise money for cancer research” stuff. Completely useless. We were in the habit of just deleting the glurge without comment because she was, after all, the Associate Director, and why make trouble? Then one day a new-ish employee got one of these and Replied to All with a link to the American Cancer Society and a terse statement about not wasting her time with useless glurge. And lo, the useless glurge stopped and Was Seen No More.
Lesson to employers: always have one employee with Asperger’s Syndrome on hand to deliver all the terse “stop wasting my time” messages people need to hear. (No, it doesn’t take someone with AS to deliver a message to keep people acting professional, but it’s funny what we let people get away with for fear of looking like a jerk, isn’t it?)
Years ago, before people who sent company wide emails with a distribution list in the Bcc section, we would have morons that would hit “reply all” and ask to not be included on the distribution anymore. This request of course would go to everyone in the company. This would then be followed up with several “reply all” with “me too” requests.
I asked our HR director if this was his method of determining the next group to be laid off. They finally started putting the distribution list in the Bcc section.
I have used up every little bit of willpower I have reading this thread. Fortunately, it was enough to keep me from PMing MeanOldLady, including only the text of her OP and adding the subject line ‘FYI’.
I’m very proud of myself.
Several people did this. You would not have been alone.
Damn it! I thought I was being original.
Because you’re a Mean Old Lady! 
Before trying the passive-aggressive approach, if what he is doing really annoys you, I would first try the direct approach. For example, in this case,
I would send him a reply that says “Why are you returning my e-mail back to me with FYI?” If he doesn’t answer the e-mail, then call him on the phone or walk over to his desk, asking “Why are you returning my e-mail to me saying FYI”?
Then, if he keeps on doing it, try your random e-mail approach.
At least that’s the way I would handle it.
I have a colleague that’s done that to me sometimes. An e-mail going out to X,Y,Z asking Question A. My colleague involved in this project will forward the e-mail to me. I just reply to my colleague saying “I was on the distribution list of the original e-mail.”
Ha ha! These seem like good (and hilarious) ideas, except the one about walking over to him, considering we are several states apart. I could tell him to knock it off, as I have told him to knock off several other annoying habits in the past, but it wouldn’t amuse me as much as sending him completely content-free e-mails. You wouldn’t believe how much I giggled FYIing him on the company-wide memo we got yesterday.
There’s really no downside to this. It makes me laugh, and he won’t get mad because he thinks I’m the cat’s pajamas. As much as it may seem I hate him, I don’t, but goddamn he annoys me with that FYI business. Now it’ll amuse me. Best case scenario, of course, is he’ll get the hint and stop.
And why is walking over to him a bad and unfunny idea? Don’t you feel stuck in your soul-crushing job? Do you want to grow old (well, older, I guess you already are old according to your poster name) without ever having had an adventure?
I suggest you try this. For the next 7 days, I want you to say “Yes” to any question people ask you or any proposal you get. You are not allowed to say No to anything. See what happens! (It worked very well for Jim Carrey).