Especially with your cousins cost basis of zero.
Just playing devil’s advocate here:
What if he buys a car with that bitcoin and those utxo’s find their way back to the exchange. Do you think the utxo’s wont be tracked back thru chainalysis to you? Knowing that you bought them originally and now it’s clear that you no longer custody them. I guess it would depend on how far “they” dig. Time will tell I suppose.