Yes I have a friend who was widow on enemy team (I'm pharah) and I kept killing them repeatedly they eventually said they'd stop trying to snipe me if I stopped attacking them.
Happened when I was Mercy a couple weeks ago, they invited me to a party, told me they were pissed but they told me I legit carried (I definitely didn't but I'll take the compliment, ya feel me?) then we played comp for a bit.
Wha'ts more interesting is when you've kept the losing team on somewhat equal grounds for as long as you could. Then you get multiple friend requests at the end of the match. lol