Fat Tony said:
Let me ask you all a question. If your friend is getting killed playing, and he's down to his last $20, would you do it to him? And if you say yes, tell me that friend wouldn't have a problem with it.
I don't know what you mean by his last $20. Do you mean his last $20 to lose for the night? His last $20 in his pocket and bank account? Actually, what you mean is irrelevant.
As all things in poker, it depends. I check raise his ass 100% if I think I have the best hand and he'll bet and call my raise. I however would not check raise him if the pot was large and I was on a bluff because he couldn't reasonably lay his hand down.
I do not know your friends but my friends and I play poker for the comaraderie and competition. Very few play for $$ (although $$ is the only way to keep score). Most of us are competitive and to play "soft" would be seen as weak. To answer your question, in our game as long as a play abides by the generally known rules of the game it is ok and no one will get upset.
Once a new player to the game got upset with me for a check-raise and I proceeded to say "if you don't like it, then don't bet behind me." The other players jumped on the guy and said that everything is ok as long as it doesn't violate a rule. For me, the free cards are worth way more than the extra bets from the raise.
The most important thing to remember is that no one I play with plays poker for his "last" anything. We play stakes that are quite meaningful but no one will be bankrupted by playing for a night. When we play and someone gets buried, we ALL feel bad but take comfort in knowing that he will be back to drink and have fun the next week or month.
BTW, the one rule that we do not follow is verbal string betting. We don't have angle shooters so we use "best" judgement regarding this. If someone says "I call and raise" we let him raise despite the fact that in most poker rooms this is a no-no. IMO, a string bet is much worse than a check raise.