Any great fighter in the last fights of their career, getting beaten by some no mark as if they were journeymen i.e. Ali, Joe Louis, SRR, Tyson, Sweet Pea, Benn etc
Honourable Mention to Smoking Joe for the Thriller in Manila, there was the classic fight with no loosers. For someone to go through that much, to give what he gave and to loose in the way he did is heartbreaking. Fights like this are what make boxing great, don't begrudge them a penny of what they earn.