Midtown High must've had a helluva Home Ec. class, if Peter and Flash can both knock out costumes.

It doesn't necessarily follow that Flash's costume design would be so close to Peter's, though. From 2018, What If? Spider-Man #1, "What If Flash Thompson had become Spider-Man?" Written by Gerry Conway, pencils by Diego Olortegui, inks by Walden Wong.

I might as well be wishing for a pony here, but I wish What If? still had regular numbering, instead of a big pile of #1's or event-related mini-series. This particular issue was after, um, whatever mini-series where the original Nick Fury got sent to live on a farm upstate was made "the Unseen," to live on the moon and bear witness like the Watcher used to; which included What If? hosting duties again. (It was Original Sin, and the numbering on that one looks a mess.) Oddly enough, Marvel had done a version of Spider-Flash before, in What If? #76: Peter takes a bit more hands-on approach to deal with him there, and that was the last issue of that series with Uatu hosting.

The trigger event of Flash attending a certain science fair, leads to him getting the powers, at least two deaths, and a lot of excessive force: Flash wasn't a scientist, so his Spider-Man doesn't seem to have webs. Still, he seems more accepted as a hero, in large part by the endorsement of J.Jonah Jameson, despite the fact that Flash had not saved JJJ's son John. (It's unclear if Flash had tried and failed, or wasn't there.) Peter Parker was still taking pictures of Spider-Man, since he needed the money for Aunt May's blood cancer treatment. But, when the isotope needed for that is stolen by the Master Planner, Peter follows a tracker he had placed on Spider-Man, to Flash's trailer-park home, and discovers Flash's secret. Flash does not take it well, as he had a lot of resentment towards "smart guys" turning people against him, and lashes out, killing Peter with one punch.

Stunned, Flash tries to redeem himself by tracking down the Master Planner and getting the isotope; but long-time readers would remember, the Master Planner was Doctor Octopus! Flash takes out a load-bearing pillar in the fight, setting up the traditional "Spidey lifts heavy stuff" moment, but not by overcoming self-doubt like Peter had to, but by acknowledging he was not a hero, and would have to make amends. In the end, Aunt May is saved, if devastated at the news that Peter was dead; and Flash turns himself in to face the music. (I feel like Flash wouldn't really defend himself, but probably wouldn't serve a lot of time: the government or S.H.I.E.L.D. or something would put him to work.)