Pick a fight with someone bigger than you

There's nowhere to run! Fighting in close quarters against a bigger opponent will not turn out well
for you.

Check out talent in the mirror

Remember steel doors are reflective too. So if you are behind her checking her out, often or not she can see where your eyes are going. Not cool.

Break wind

Really, this is every lift-user's worst nightmare. You may seem to be in perfect solitude for now but there's no telling who'll pop in on the next level after you've gassed the place.
Ditto for burping.

Make annoying small talk

It's a social dilemma being crammed into a box with complete unknowns. Everyone feels obliged to chat but it's a lift, not the Big Brother house.

Bring your Doberman along

Why don't the two of you just wait. No one's objecting, but that's only because they are scared.