I've had a few people who don't know me well address me using "omae" recently. I've always mentally equated "omae" with the way some Londoners often use "c*nt" as in "How are you, you old c*unt?" to a friend or "See here, c*unt, you don't understand" if you want to raise the temperature a tad.
One time, a young bloke (twenties) was clearly intending to be rude but, since he got up and left the bar, nothing was made of it. A second time, in a different place, the bartender jumped in and told an older bloke (mid fifties) who had started talking to me that it wasn't nice to use omae. He looked mortified and apologized before carrying on. Five minutes later, we were back to omae but, since he was drunk and seemed like he meant well, I didn't see any point in picking it up again.
The other day, sadly at yet another bar, a drunk in his forties joined in a conversation I was having, using omae. The bartender near me smiled indulgently and said to him "What's with all the 'omae'?" and then said to me "He's a good bloke so don't worry". He was OK and it transpired he was trying to invite me to a party his wife was holding which all the other barflies were going to attend.
A customer next to me didn't want that to be the end of the affair and again admonished the bloke for kicking off with omae. The bloke replied that he didn't mean to be rude and that he was the kind who always called a spade a spade so if he was trying to be rude because he didn't like me, everyone would soon know it. Again, he seemed all right so it nothing came of it. After he left, the customer next to me apologized if he'd put me on the spot by having a crack at the bloke but he said he didn't like people who didn't show respect because it could easily turn nasty further down the track.
I've generally reacted by ignoring strangers who start calling me omae but it hasn't happened that often. In the recent cases, I haven't had to say anything because other people have jumped in to fight my battles but I have started wondering whether there are any good natured ways that other FGs have used to draw attention to an unwelcome use of omae should the occasion arise.