Geez... last 5 1/4" I bought? It was probably 1990.
I don't remember buying any 3 1/2" disks after '94-'95... Although PC stuff I bought still came with them for drivers etc. maybe as late as 2000.
What I miss is soaking an entire box of Ohio blue-tip strike anywhere matches in acetone until the heads sloughed off. Mixing up the paste, and painting a carefully razored apart diskette with it, except for the one wedge that was visible through the disk window. Then carefully re-assembling it, and labeling it with something like "Playboy .GIF's" then leaving it somewhere at school...
It never burst into jets of flame like the Anarchist's Cookbook claimed it would, but it did smoke nicely.
Wiring up a model rocket ignitior taped to the fuse of a small colored smoke bomb to an RS-232 port and putting a .BAT file called "SMOKER.BAT" that read:
echo off
dir > com1
smoker.bat
That really created an impression.