Because Singed kills heroes usual a poison trail behind him. It's an embarrassing way to die. Usual scenario :

1. Newbie sees Singed at half HP and chases him.
2. Singed runs off with his poison trail on.
3. After chasing awhile, newbie notices his HP has gone from full to less than half.
4. Newbie turns back. Singed activates MS boost and chases newbie.
5. Newbie gets tossed by Singed.
6. An ally has been slain.
7. Newbie's teammates starts to question newbie's sexual orientation and parents' marital status.