(source: Iceberg Slim- Pimp, The story of my life)

Now I met a whole section that has parts I am completely at sea with. Below I quote the section and underline the fragment that I cannot interpret:

"I held the end of a necktie in my teeth. I coiled it and tightened it around my arm. On first stab I hit a perfect bullseye. I did Top's jackoff bit. I threw up. I just made it to the john. The kick was greater that the one at Top's"

background:

Slim describes how he bangs cocaine after learning it from his friend Glass Top.

'Top's jackoff bit' may refer to some special technique of using the syringe to get the drug into the vein most effectively. But the other underlined parts...well, I have no idea. Anyone has?

many thanks in advance