There is no foolproof way of avoiding bumping into your students in the street and the more you teach, the worse it inevitably becomes. There are a few ways to minimise seeing students outside of the university, especially when you’re in compromising situations, like; drunk, eating or making out with a stranger.
Drunk or otherwise impaired is the worst way to bump into a student, especially a current student, because your memory and judgment is inhibited and you’re probably not going to remember their name. Don’t worry, if they’re a girl, their name is probably Laura, or Lauren. If they’re a boy, their name is probably Michael or John. Mumble the most appropriate sounding of these options, and hope that they’re drunk too and don’t notice. It’s also important not to choose a bar heavily frequented by undergraduates (or anyone else under 20). This is probably something you do anyway, but sometimes they sneak in unexpectedly. Therefore, avoid drinking within a 2km radius of the university you teach at. This will help you avoid the students who live on campus, who are the worst because they’re the richest and the most obtuse. The only exception to this rule is a pub near campus so scungey and full of old men that an undergraduate would never enter it. If there is one of these, make it the secret drinking destination of choice after class.
Trendy bars and cheap bars are also very dangerous, but the danger should probably be endured because what are you doing in a bar that is neither trendy nor cheap? What sort of research student are you anyway? Medieval Literature?
Avoiding students when eating out is a problem because undergraduate students either enjoy impoverished eateries for the charm, or are actually impoverished, like most graduate research students. Try to convince the nice waiter at the dumpling place that you need to sit in the darkest corner of the room if you see a student approaching, clutching at their $5 long neck of Tsing Tao. If your student still spots you, and is not content to politely wave, try not to have a mouth full of food when they approach, their clothes are probably more expensive than you can afford, so you probably don’t want to spit food on them. The fortunate part about eating somewhere extremely cheap, is that the restaurateur is all too happy to be rid of you, so they can peddle their steamed carbs to the next table of half-drunk hipsters. This means that you can excuse yourself from a conversation with your student at any time with minimal apology, and leave quickly without being notably rude.
Finally, it can be quite awkward to be found making out with someone in the dark corner of a bar by a student. (Or really, by anyone, especially if they have a camera and access to the internet.) The best way to avoid this, is not to be a such a skank that you would do that in the first place. But failing that, just make sure the person you are making out with doesn’t suddenly become one of your students. Or you may have to dob yourself in and wear the shame of double-marking.