I've been in the same place as Spencer Matthews (literally next to him) twice, and he had no reason to be nice to anyone as he wasn't there in any public capacity but he was totally charming - friendly, helpful, kind, no look-at-me attention-seeking, really down to earth and approachable.
He's a raging narcissist as was very apparent if you watched Made In Chelsea. He has the capacity to be ultra charming when he wants to be.
This is him breaking up/rowing with his then gf Louise who he had treated horribly - the whole seen is revolting and he is vile to her and in this clip here he says to her (an upset & hurt young woman who loved him):
"it's fucking hard to respect you when you allow me to cheat on you" and "you are going to go home after this and cry your fucking eyes out and I hope you do"
Anyone who is capable of speaking to another person like that let alone a former intimate partner is really not at core decent or nice.
And the whole "I've changed/grown up/its a long time ago" doesn't wash with me because it's about a fundamental moral value of how you treat people. I've never spoken to anyone like that in my life and even when very young if you are breaking up with someone who loves you, you know they are hurting. It's a very nasty streak in someone to behave like that IMO.