Being a nice reviewer

Even though you feel obliged to reject the paper you are reviewing, you still can
1. Encourage the author to re-submit it as a poster and give them the chances to do so.
2. Say it is a novel and interesting idea although there remain serious flaws in the paper.
3. Extend an invitation of redirecting the submission to a parallel workshop if you find value content in the paper.
4. Insightfully tell the authors where the specific problems are and how to improve the paper like an expert.
5. Don't reject paper for tiny flaws, marginal issues. You can always find fault somewhere.