Worst combos by far have to be fighting game "tutorials."
I'm actually still pretty good at fighting games, but I rarely ever successfully do any of the combo tutorials beyond a couple of combos.
Absolutely ridiculous combo tutorials in damn near all fighting games.
Things like: light Punch, hard kick, medium punch, light kick, hard kick, medium dragon punch x 2, hard fireball, x 3 then light punch, hard kick, medium punch, light kick, hard punch, light punch, hard kick
All in about 3 seconds according to Tekken7, Soul Calibur 6, DOA 6, all with completely ridiculous combos.