Anything goes on testnet - it is very cheap with the new bitcoin relay rules to spam testnet tx, for better or worse. If you can break testnet with tx spam, then it is a canary-in-the-mine for Bitcoin, so you might watch the way that Bitcoin becomes harder to use under such load and make your own bug reports if you can quantify.
I've been seeing large 'inv' messages for transactions on prodnet as well. When you send a 'getdata' request to the node, though, it doesn't respond. I've also been getting incoming connections that don't respond to a 'version' message and just disconnect and then connect again.
I had one yesterday that did this continually until I banned the IP address.
And, of course, my favorite which sends dozens of double-spend transactions one after the other in rapid succession.
