I have indulged in a Miller lite or Rolling Rock once or twice while mowing or brush hogging. Some times 2, over the coarse of 4 or 5 hrs. Two beers over 4 or 5 hrs is my absolute limit while operating on my property, one beer more often, and ice water most often. One thing worth mentioning is that if you are drinking and mowing whithin the right of way of a public road, {mine is 30 ft from the road centerline} you can be cited for an open container violation. I never have been, but my mother was an insurance agent for 19 years, and had it happen to lots of her clients.
Bottom line is know your limits, I am 6ft and 220 lbs, and almost always have a full belly[see 220 lbs]. I can handle 2 beers much better than my 120 lb wife, who would be in no shape to operate after 2 beers.