Things like "I've noticed you have a fine reputation"; "you have a reputation for a discerning eye"; "several important people told me you're a good agent" and/or "you've drunk three editors under the table and lived to tell about it"
We both know the score. You're a writer. I'm an agent. You want me to read your query. I want to find good stuff.
No hot-to-trot mating dance required.
In fact, it's counterproductive.
About the only thing that doesn't make me reach for the barnyard shovel is if you compliment my clients' books (and it's clear you've done more than lift the title off the blog) or you've read enough of this blog to actually get something out of it.
Those I pay attention to.
The others just annoy me cause sucking up in so clueless a way makes it look like you think I'm