Sometimes, it's good to do this as well.
In 6 years of being a gym rat, I can say I had only two "personal' wars, in the midst of
a lot of intense sparring.
Both were against bigger opponents. I was 5,10", 154-160 lb.
One was with a white guy named "Lincoln," who was green, but big @ 6', 205. He was physically-gifted, intense, but green. He liked to burn all his energy in the first round, and made a lot of fellow-beginners quit.
I was the opposite, like a "poor man's" Chavez ... I would always came forward, and put steady pressure (for the first round or two), but didn't do too much — just trying to get the pule going + a read on my opponent
under fire — after which I began relentless work.
Long story short, at the end of 1.5 rounds, "Lincoln" was done, quit in front of his team, and never came back to the gym again. I had humiliated him (he brought his girlfriend, in front of whom he quit

)
The other was an Hispanic guy named "Harry," who was experienced, and also strapping/big @ 6'3", 185. He (like some on this thread) complained about "how hard" I went. In the opening round, the 6'3" Arroyo came right after me, at 5'10" — and within maybe two minutes — click me with a straight right, causing me to fall back, and had it not been for the ropes, I probably would've went down. (I've never been knocked-down, ever, in six years of sparring pros. That time, if the ropes weren't there, I quite possibly would have fallen.)
Still, it didn't mean shit, as I was fully-aware of what was going on. It was an immediate "gym war" — toe-to-toe exchanges, the whole bit. No one went down, no one was knocked-out. (I had some blood under my left nostril, his nose was broken, and his mouth was bleeding into his T-shirt.) It only went two rounds, because both our trainers told us to STOP — DON'T MAKE THIS
PERSONAL! "Harry" and I spoke afterward, and he criticized me for "always going so hard" — and I told him, I am training to
fight,
not "be friends."
I also reminded him he was 5" taller than me, with a significant reach advantage, and there is no way in hell I could compete with him "boxing on the outside." I had to be willing to take three hard shots, to back him up, get him against the ropes, and try to beat TF out of him in-close — especially since
he dropped me, within the first two minutes.
We shook hands and each understood the other better after that. No bad blood.
(Which was a good thing for "Harry," because I had begun to train in Gracie jujitsu at that point

)