I'm not sure if this has been posted before, I did a search for arena and drink and it didnt give any results that matches this, anyway, lets get to the point.
This has most use in 2v2 against caster teams but it works in all brackets with a little luck. First prepare a macro with /sit, then sign arena. Once you are getting low on mana and start drinking have your trigger finger ready on you /sit macro and when any opponent comes close to interrupt your drinking spam it, voila, your drinking wont be interupted.
Limited use against an MS Warriorsince when you sit you will have 100% to be crited no matter how much res you have.
Enjoy while it lasts, and sorry if its a RP