Q:  I've heard people boast how they can take on 10 or so people in a fight when they're pissed off. Is this just used as an intimidation device?

A:  
Wow, I'm not sure who they are trying to intimidate.  Multiple attackers present one with an extremely, extremely dangerous situation -- particularly when the attackers are pre-teens and teens.  Studies show that attacks by a pack of subjects is more likely to turn into a homicide when the attackers are juveniles.

When we run multiple attacker drills, everyone is pretty much toast if you cannot manage to string out the attackers and punch them out one by one.  Once one or two of them grab you, you are going down.  

I fought four guys once on Wilshire Boulevard in L.A. and got one good punch in before I went down after being tagged about three dozen times from all angles.  On the other hand,  I fought two guys at one time in a bar in L.A. and beat the crap out of them before I got tossed out by the bouncer (man he was good too -- I went sailing out of the door before I could figure out what was going on).  The Wilshire Blvd. guys worked me over all at once.  The two guys in the bar came at me one at a time.  So I guess it depends how the bad guys decide to play you.

Ironically, streetfighter Tom Proctor feels that he would rather be attacked by more than three attackers than just two because the larger number of guys actually get in each other's way.

But I would not count on that.  My general rule is that you fight multiple attackers with your weapon. Even the biggest names I've trained with DO NOT advocate fighting multiple opponents without a weapon.

Your choice of the word "boast" is telling.  My B.S. meter goes off most of the time when I hear people like this.