If a solo male goes to Thailand,absolutely everyone understands why he went there. That's why I wouldn't go without my SA. Certainly expect a grilling from the home-town border guards
This is utter bullshit, been to Thailand twice alone and the customs don't even look at you. As long as your paperwork is in order, they stamp your passport and you're on your way, no questions, nothing.
As for safety, the only time I ran into trouble was through my own stupidity, rang the bell in a Thai karoke bar and didn't have the money to pay, BIG mistake, 3 of them followed me to my hotel to get the money. But expect to be ripped of by motorbike taxis and the girls if they figure out a way to. I passed out drunk a couple times, only to find money, cell phone and lap top gone when I woke up. I was at a hotel that didn't take their ID, I moved hotels. Always make sure the hotel takes the girls ID.
In Thailand, if you keep your nose clean you can have the most fun you will ever have, but if you do stupid shit, you could easily wind up in a shitload of trouble, or dead. I saw a couple guys making fun of a few ladyboys, next thing you know one of them had about a 4" gash on his cheek, shirt covered in blood, needless to say his vacation was over.