For the first-time, this happened to me on Saturday.
Early in second-half, player whom I'd spoken to earlier regarding his... attitude... recklessly tripped an opponent. Simple caution. Hit whistle and call him in, "yes, please number five." His reaction was to shout "well I might as well just leave now". It wasn't remotely close to DOGSO, so no idea what was going on other than him massively throwing his toys out the pram. Despite whistle and vocal suggestions that he should probably come back towards me, he just wandered off, removed his shirt and stood off the pitch.
Captain wouldn't confirm his name either and suggested that they were "going to make an unofficial substitution". I refused on two grounds: a) I'd allow a substitution only when I'd finished the cautioning process, and b) they didn't have any substitutes anyway. Bit more back and forth of attempting to acquire/confirm the player's name.
Showed yellow, paused, moved closer towards the #5 then showed yellow-red. See ya, fella.
Wanted to come back on 15 minutes later, amusingly.