In addition to these disapproved behaviors:

• f4f: I follow you, please follow me
• begging for upvote: I upvoted your post, please upvote mine
• upvoting at 100% your own "nice post" comment

I just have been witness to another bad behavior:

Bribing for Upvote

source

Somebody sent me 0.001 SP with this memo:

• Bussines proposal: Hi vcelier If you upvote this post with 100% of your voting power I will return to you 50% of the steem dollars from that vote as soon as I get paid: (followed by a link to his post)

I absolutely dislike this kind of attitude.