Mac pho is actually delicious, I fear you have been the victim of a totally gross and biased tradition. Yup, I'm talking about spitting in the soup. It's not a rumor but is actually fairly common and kind of a harmless bit of humor or prank played on male falang expats from Thailand.
Some common avoidance strategies are to not speak any Thai, use Lao or even better only English and be sure to mention that it's your first time in Asia and you are on your way up from Cambodia or Vietnam or Singapore or something.
I have a buddy who taught me this game called "spot the spit" that he played in Vientiane where many expats from Thailand go to make their visa runs. He'd watch a falang loudly saunter in, Thai "girlfriend" and various hangers on in tow, watch the cook ladle up a large steaming bowl of pho, then there would be that short second of losing sight of the bowl, a back turned or a moment in the back room accompanied by that unmistakable coughing or a clearing of the throat. Then, voila! A smiling waitress appears bowl of pho held high like some kind of reverent offering to the unsuspecting falang, or farang as they are called across the river.
Some say it's harmless, all in good fun, one has to be able to take a joke. I don't know that I've had the pleasure, but I suspect it adds a note of sour to the soup. How do you find the taste?
Somsai - well, I didn't go more than once. I don't like the ****. It's on my long list of SEA foods I don't like. That list is WAY longer than the list of what I do like.
I'm kind of popular around here, so it's tough to believe. But I'll admit you never know.
Pho is crap. Sorry.