Sorry, Metal.
The old "OMG ITS A GAME" excuse doesn't justify OP weapons. I got 12 loving heads as a Demoman, ran into groups of people with 'Targe, never entered red health. Kinda ridiculous.
Not to mention it steps out of Demoman's class boundaries.
Oh god. Either you were in a random pub or your fav. server is full of untalented newbies.
Saying you got x heads/kills/captures or whatever isn't worth anything because you can't be sure about the skill level of the enemy team on pub and most people don't work together there anyway.
Anyone who is good will rape your face off when he sees you.
It's not like totally impossible to kill someone who has equipped a melee weapon, no matter how fast and how much HP he has.