Is this considered a offense ?

I would call that unnecessary, intentionally crass/disgusting, and rude, personally. I would recommend not saying that.

[{quoted}](name=DISHONORABLE XD,realm=EUW,application-id=ZGEFLEUQ,discussion-id=cZccdk7W,comment-id=,timestamp=2017-10-08T19:54:24.513+0000)

to gently ask my teammate who banned my pre picked and then fed in game , to eat my hemoroids ?

yes

I'm confused I thought you couldn't ban someone who already has the champ pre selected