Bar staff's uniforms accidentally endorse a very specific sex act.
Usually "keep calm" is something that is said right after "try anal."
Even without the odd photo angle cropping out the last letter, the creater of this t-shirt did not really think this through. Mostly because every dumb drunk who stumbles in will immediately make this joke loudly and repeatedly until he's had enough ales to get kicked out onto the street again — twice as often to any female bartenders who are unfortunate enough to be seen in this shirt by drunk males. Secondly, in a panic situation, you don't want to try a new ale anyway; you reach for something comforting you already know. Finally, the whole "keep calm and carry on" thing is as over now as the war it was designed for.
Sources: Huffington Post