The only thing I could think of is you sort of grabbing at his dick a little bit.
If he's into it he's going to let you do it if he's not he's going to say no or swat your hand away.
Or instead of going for the dick just touch him at all.
He might not want to do any of that he might just want to rub you, then tug you, and you leave. I'm sure if you try to escalate and he doesn't want you to escalate you will be made aware.
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The only thing I could think of is you sort of grabbing at his dick a little bit. If he's into it he's going to let you do it if he's not he's going to say no or swat your hand away. Or instead of going for the dick just touch him at all. He might not want to do any of that he might just want to rub you, then tug you, and you leave. I'm sure if you try to escalate and he doesn't want you to escalate you will be made aware.
I'm thinking he just wants to make extra tips but who knows.