Big servers and guys who go for broke all the time.
I played an opponent the other day who had a big serve yet an even bigger ball toss which meant he would do so inaccurately and catch it again, at least five times a service game and sometimes two or three times before one serve. When it went in, it was extremely difficult to handle since he put plenty of kick on it, along with his pace, and we were on a synthetic grass court that was way too sandy so the ball was kicking up really high. I had barely any rhythm at all on his service games and he's the kind of player who wanted to crush a forehand off every one of my first and second serves. I won in straights (5 and 3) but it wasn't exactly fun, there were very few meaningful rallies and I just couldn't play the game I wanted to 'cause his inconsistency and 'in your face' play stopped me from doing so.
It didn't help that I broke a string in warm up and had to borrow one of his to play, it was the first time I've used the K90 so I found it kinda tricky to play with since I've used 105sq for several years and only recently started playing with the K Blade 98.
I don't mind playing pushers, I enjoy being able to attack and take control of the rallies. I'm still trying to get my serve back after a long layoff, I've completely forgotten how to hit a flat first serve and have since resulted in kicking/slicing both first and second serves. My kicks are still attackable though so it's something I'll need to address asap.