I have had this happen - in the early days of DC being at school.
When they were 5 to 8 y.o. DH worked night shifts (10-6,) and mornings (6-2,) so he was always there to get the kids from school. I worked 10 til 4. Monday to Thursday. I had no choice in those hours. DH told me about this mum and that mum who chatted to him at the gate whilst waiting for their kid(s.) Fine. No big deal.
I took them to school and DH picked them up. After several months I had a couple of weeks off, and went collect DC from the school with DH. One woman (who was waiting for her kid,) saw my husband, and said 'HEYYYYY STEVE!!!' with a big
'what a wonderful sight to see!' 
Then 5 seconds later she saw me, and her face hit the deck. 'Hi' I said with a big smile. She was about 8 inches taller than me, and looked down at me as if I had shit on her cornflakes. Like I was pure filth. She didn't even acknowledge me! 
Then I turned up again the next day with my husband - ya know, to meet my own (and my husband's) kids out of school, and she made a beeline for him and completely ignored me. Again. They chatted for 5 minutes, both ignoring me. This was my HUSBAND.
When walking back, I said 'I don't think she likes me.' DH said 'don't be daft, she just doesn't know you.' I said 'well she doesn't know you either does she?' He said 'yeahhh but we chat a lot.'
Seemed to me, she had designs on him, and was really angry when his WIFE came. Not sure if he liked her. I think he was genuinely just being friendly, but couldn't see how he was coming across (that he may be interested in her.)
On the third day it happened again. So I butted into them chatting and said 'hey I am here ya know' with a big grin.
'You can talk to me too, I am Steve's wife! I am friendly too.' 
They both just ignored me, and carried on talking! 
So, on the fourth day, I told DC to come out of the South entrance and not the North. I went with DH to the North, and this woman was there again, and they both ignored me... So I walked off. About 20 seconds later - (yes it took that long!) - DH called out 'where you going?!' I ignored him again.
I bolted to the South Gate, met the kids, and walked home (10 minute walk.) DH texted me about 5 minutes later and said 'where are you?' I texted back and said I was home with the kids, and said he had absolutely no right to treat me this way... chit-chatting to this bloody woman, who blatantly ignored me, and doing nothing when he could see I was upset.
He said 'well she's my friend, there's no reason for her to talk to you really. Maybe she just doesn't want to be mates with you.'
Unbelievable.
I told his mother about it that night, and she went loco on him. Said he was the worst husband ever, and needs to treat his wife - the mother of his children - better than this. Otherwise, don't be surprised if she leaves you and takes the kids.'
He protested and said she was just his 'friend.' MIL said 'don't be fucking naive! She is after you, and Sarah (me) can see it too, and you're loving it!' At one point I thought she was going to hit him. 
From then on, DH went to another place to meet the kids, and when he DID see this woman, he ignored her and just looked at the floor. She was incensed, and said to him 'wife got you where she wants you eh? Not allowed to talk to me?' 
DH did acknowledge he was in the wrong (a few weeks later) and said he was sorry. He also said when this woman sees him now, she scowls at him. Stupid cow. Must have thought she had a chance with him! As I say, he thought he was being friendly, but it seems she saw more into it, and saw me - his WIFE - as a threat. But them two both chatting and ignoring me made me really angry and upset.
Glad when DC left 'little school' to be honest. The 'school gate' experience was not nice, for a number of other reasons too...
We were both quite young (early 30s) when this happened. No WAY would I have been so nice and tolerant now. I'd scream 'who the fuck do you two think you are, fucking ignoring me like I'm not there.' And fortunately, DH has better manners now!